Referencing glossary

This glossary explains common terms used in academic referencing and citation systems. Whether you’re editing a bibliography, checking citation accuracy, or learning how different styles work, these short definitions will help you understand the basics of referencing and reference editing.

This glossary will continue to grow as we add more terms related to referencing and academic publishing.

APA

APA style is a referencing and formatting system created by the American Psychological Association. It is an author–date style (also known as a Harvard-style system), where in-text citations include the author’s surname and year of publication (for example, Smith, 2022). APA style is widely used in the social and behavioural sciences, including psychology, education, business, nursing, and linguistics, and is one of the most common referencing styles in academic writing.

Read our guide to APA.

author–date system

The author–date system (also known as Harvard) is a citation system where in-text citations include the author’s surname and the year of publication, for example ‘(Smith, 2022)’. Full details of each source then appear in an alphabetized reference list at the end of the document. This system is used in styles such as APA and is common in the social sciences, natural sciences, and many interdisciplinary fields.

author–number system

The author–number system (also known as Vancouver) is a citation system where sources are assigned numbers, and those numbers are used in the text instead of author names. The full source details appear in a numbered reference list, usually in the order sources are cited. In-text citations may appear in brackets (e.g., ‘(5)’ or ‘[5]’) or as superscripts (e.g., ‘⁵’). This system is used in styles such as AMA and IEEE, and is common in medicine, engineering, and the physical sciences, where concise citations and easy scanning of references are especially important.

author–page system

The author–page system is a citation system in which in-text citations include the author’s surname and the relevant page number, rather than the publication year. For example: ‘(Smith 56)’. This system is used in styles such as MLA, and is common in the humanities, where the precise location of a quoted passage is often more important than the date of publication. Full publication details appear in an alphabetized reference list or bibliography at the end of the document.

bibliography

A bibliography is a list of sources consulted or relevant to a piece of work, whether or not they were directly cited in the text. It can include background reading, recommended sources, or works that informed the research but were not quoted or referenced explicitly. This contrasts with a reference list, which contains only the sources that are cited in the text. Bibliographies are more common in humanities disciplines and in styles such as Chicago (notes and bibliography), while reference lists are typically used in author–date systems like APA and many scientific styles.

citation system

A citation system is a method of showing sources within the text that links to full details elsewhere. The four main systems are: author–date (e.g., ‘Smith, 2022’), author–number (e.g., ‘[5]’ or ‘⁵’), author–page (e.g., ‘(Jones 56)’), and notes that use footnotes or endnotes (e.g., superscript numbers leading to notes). A citation system governs how you cite sources in the body of a document, whereas a reference style or style guide (such as APA, MLA, Vancouver, or MHRA) provides broader rules, including how to format the reference list or bibliography, punctuation, capitalization, and other presentation details.

DOI

A DOI (Digital Object Identifier) is a permanent, unique identifier assigned to a published work such as a journal article, chapter, or dataset. It provides a stable link to the official version of the source, even if the website or URL changes. A DOI looks like 10.1038/s41586-020-2649-2 and can be turned into a direct link by adding https://doi.org/ in front, ensuring the reference remains easy to find and verify.

et al.

Et al. is an abbreviation of the Latin phrase et alia, meaning ‘and others’. It’s used in in-text citations and reference lists to show that a work has multiple authors without listing every name, typically after the first author (e.g., Smith, et al.). Some styles guides require et al. to be italicized, while others do not, and some style guides require a comma before it, while others do not.

in press

In press refers to a work that has been accepted for publication but has not yet been formally published. This means the content has passed peer review (if applicable) and is in the final stages of production, such as copyediting or typesetting. When citing a source listed as in press, the year may be replaced with ‘in press’ (e.g., ‘Smith, in press’) because a final publication date is not yet available. This term differs from preprint, which refers to work posted before formal peer review and acceptance.

in-text citation

An in-text citation is a brief reference placed within the body of a document to credit a source and point readers to the full entry in the reference list or bibliography. Different citation styles use different formats. In the author–date system (used by styles such as APA), an in-text citation typically includes the author’s surname and year, such as ‘(Smith, 2022)’. In the numerical system (used by styles such as AMA or IEEE), sources are cited with numbers in brackets or superscript, like ‘[5]’ or ‘⁵’. In the author–page system (used by MLA), citations usually include the author’s surname and page number, for example ‘(Jones 56)’.

issue number

An issue number identifies a specific part of a journal volume, helping to locate where an article was published within that volume. Journals are typically organized by volume (often corresponding to a year) and then divided into issues (for example, monthly or quarterly releases). A reference may include volume and issue numbers, such as 15(3), meaning volume 15, issue 3. Not all journals use issue numbers (some publish articles continuously within a volume) but when they are present, citing them helps ensure precise and accurate referencing.

MLA

MLA refers to the citation style developed by the Modern Language Association. It uses the author–page citation system, meaning in-text citations include the author’s surname and page number (for example, ‘(Johnson 42)’), rather than the year. MLA is widely used in the humanities, especially in literature, languages, cultural studies, and related fields. Full publication details appear in an alphabetical reference list headed ‘Works Cited’ at the end of the document.

reference list

A reference list is a list of all the sources that are cited directly in the text of a document. Each entry corresponds to an in-text citation, allowing readers to locate the exact works referenced. This differs from a bibliography, which may include additional sources consulted for background reading or further context, even if they are not cited. Reference lists can be numbered (usually sequenced by the order they are cited in the text) or alphabetized by the first author’s surname.

sentence case

Sentence case is a style of capitalization in which only the first word of a title or heading is capitalized, along with proper nouns. For example: The history of microbiology in Europe. Sentence case is used in styles such as APA for article and chapter titles in reference lists. It contrasts with title case, where most major words are capitalized.

Thrix

Thrix is an online reference-editing tool made by Shabash Ltd that corrects, formats, and enhances citations and reference lists. It applies academic styles such as APA, MLA, Chicago, and Vancouver; checks metadata using sources like Crossref and PubMed; adds missing details; and ensures references are consistent. Thrix is designed for students, researchers, editors, and publishers who want fast, accurate reference formatting without manual checking.

title case

Title case is a style of capitalization in which the main words in a title are capitalized, while short function words such as and, of, or the are usually left in lowercase unless they begin the title. For example: The History of Microbiology in Europe. Title case is common in book titles and journal names, and is used in styles such as MLA and Chicago. It contrasts with sentence case, where only the first word and proper nouns are capitalized.

URL

A URL (uniform resource locator) is the address used to locate a resource on the internet, such as a webpage or online document. A URL tells a browser where to find content and how to retrieve it (for example, https://www.thrix.ai). In academic references, URLs are often used to cite webpages, online reports, and other digital sources that don’t have a DOI or other persistent identifier. Unlike DOIs, URLs can change over time, so style guides often recommend including accessed dates or using DOIs when available.

volume

A volume is a numbered grouping of published material. In journals, a volume typically represents all issues published within a given year (for example, vol. 15 may contain multiple issues). In references, the volume usually appears before the issue number (if a journal uses them), such as 15(3), meaning volume 15, issue 3. Books can also be published in multiple volumes.