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Subject headings - definition

Subject headings: Definition

A subject heading is an assigned word or phrase used in some databases to uniformly describe a concept. Searching using this standardized word or phrase, instead of keywords, means you do not need to worry about synonyms and spelling variations.

Example: The subject heading for cancer in MEDLINE (via PubMed) is the MeSH term Neoplasms. This means that all articles selected for indexing in MEDLINE that are about cancer at a general level will be tagged or indexed with this subject heading, or if the article is about a specfic cancer like breast cancer, with a narrower term (note: there is a time delay between the addition of records to MEDLINE and their indexing with MeSH terms, and some records will not be indexed at all).

How the subject headings are actually used in a database (if they're even available) depends on the platform you're searching, e.g., to use the subject heading for 'Neoplasms' in PubMed or Ovid MEDLINE:

  • PubMed: The search syntax is "Neoplasms"[Mesh] (You can also enter "Neoplasms"[mh] for the same effect; the safest way to use subject headings is to find them first in the MeSH Database, then to add them to the PubMed Search Builder, and then to Search PubMed)
  • Ovid MEDLINE: The search syntax is exp neoplasms/ (The Advanced Search in Ovid MEDLINE at McGill is set up by default to "Map term to subject heading", so if you type in 'cancer', you will get a list of suggested subject headings, with 'Neoplasms' at the top; PubMed does not work that way)

Keywords - definition

Keywords: Definition

Keyword (or textword) searching is when we search for words which we expect to find in the title, abstract, or author-defined terms of relevant articles; it is how we typically interrogate web search engines. Draw up a list of words or phrases related to each concept in your research question. When using this technique, you will need to be aware of synonyms and spelling variations.

Example: Keywords (or textwords) for cancer can include cancer / cancers / cancerous / neoplasm / neoplasms / neoplastic / tumor / tumors / tumour / tumours etc.

Using subject headings

We recommend the following resources if you would like to explore subject headings and search strategy refinement in more detail:


PubMed tutorials:

Using MeSH in Pubmed  (3 min 02)


CINAHL (on EBSCOhost) tutorial:

Using Subject Headings in CINAHL (3 min 32)


Ovid MEDLINE tutorials:

Advanced Search on the Ovid Platform (with a focus on Ovid MEDLINE, using MeSH subject headings as well as subheadings) (13 min 25)

See also:
Ovid MEDLINE part 1 - Starting your search (using subject headings)

Health Sciences Library, McMaster University. (2014, October 16). OVID Medline - Part 1 - Starting Your Search [Video file]. Retrieved from

OVID Medline - Part 2 - Refining your search (using keywords, operators, and limits)

Health Sciences Library, McMaster University. (2014, October 16). OVID Medline - Part 2 - Refining Your Search [Video file]. Retrieved from

Using keywords

Using keywords

Librarians typically prefer to use subject headings as the foundation of our search strategies. However, there are various reasons why we add keywords to a search:

  • New emerging research area which may not yet have a subject heading to describe them
  • To retrieve the most recent articles (which have not yet been indexed)
  • Occasionally, articles can be incorrectly indexed and may be missed by your search strategy
  • To develop a thorough search strategy for a systematic review or other knowledge synthesis

You should keep in mind that keywords do not generally account for:

  • Spelling variations
  • Synonyms
  • Plural forms

Use an asterisk * (a commonly used truncation symbol) to find variant endings of a keyword:

e.g. glaci*

retrieves glacier, glaciers, glacial, etc. We provide a fuller listing of these so-called wildcards for commonly used databases here.

Comparing subject headings and keywords

Subject headings versus keywords

Subject Headings (SH)


Pre-defined "controlled vocabulary" terms

Natural language words 

Need to know the exact controlled vocabulary term

Need to think of all synonyms, spelling variations, etc.

Less flexible. Not always an appropriate SH available

Quick & flexible way to start exploratory searches

Database looks for subjects only in the subject heading or descriptor field

Database looks for keywords anywhere in the record

Highly relevant results

Generates irrelevant results but increases the sensitivity of the search (i.e., picks up records that the subject headings may have missed)



Jill Boruff's picture
Jill Boruff
Working from home during the pandemic. Please email me with questions or to schedule a virtual appointment.

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