To summarise means to re-formulate what someone else has written (said, etc.) in abbreviated form. Whereas a paraphrase may be of equal length to the source text, a summary is considerably shorter.

Just as in quotations and paraphrases, summaries require a reference to the source.

A note on spelling: 'summarise' can also be spelled 'summarize'. In British English, both forms are accepted and in American English, the form 'summarize' is used.

Definition: Summarise (click to expand/contract)

Oxford English Dictionary

summarize, verb. To make (or constitute) a summary of; to sum up; to state briefly or succinctly.

summary, noun. A summary account or statement [where the adjective "summary" is defined in the following way by the OED: "Containing or comprising the chief points or the sum and substance of a matter; compendious (now usually with implication of brevity)"].

When to summarise

Summaries are made when there is a need to condense large units of texts or other forms of data. In summarising, the main ideas of the whole text (or a large part of it) are thus reformulated and condensed.

Students may be asked to summarise a course book or article, and scholarly articles may include summaries of previous research in order to introduce the new research that is being presented.

Although summarising is a good way of presenting in brief the contents of a certain text, theory, interview, etc., it is important to note that in a pure summary, the writer may only summarise a source, not present any new data or ideas.

Summarising is used to briefly represent what previous books, articles, etc. have expressed. Unless specifically stated in a course assignment, for instance, an academic essay can therefore not merely consist of summaries of previous studies.

Summarise or paraphrase?

For the distinction between summary and paraphrase, see the AWELU section on paraphrasing:

Advice: Step-by-step guide to summarising (click to expand/contract)

Step 1: Read

Read the text you intend to summarise carefully. Make sure that you understand the contents and the author’s argument. If it is a long text, you may need to make notes of or underline vital passages.

Step 2: Write

If it is a long text, identify the main points and list them. If the text is divided into sections or chapters, you may wish to focus on that structure when writing your summary. Then write from memory, summing up each part. 

Step 3: Check

Compare your draft with the source text to make sure that your summary catches the essence of the source text.

Step 4: Revise

If your text is too close to the source text, consider quoting certain passages. Note, though, that a quotation must be verbatim, that is, the exact rendering of the source text.

If you decide to quote, read about that here:

Step 5: Give reference

Remember that proper references are needed in summaries, as well as in quotations and paraphrases.