Keywords
The terms listed with a paper to make it findable, chosen to match how other researchers would search for it.
Keywords are a discovery mechanism, not a summary. The useful ones are the terms someone would type who does not already know your paper exists — including synonyms, the standard vocabulary of your field, and the method names you used.
Many databases prefer a controlled vocabulary, such as MeSH in biomedicine. Where one exists, using its terms alongside your own natural-language ones roughly doubles the ways a reader can arrive.