The old term used to be just Keyword where you tried to rank for a keyword but everything evolved beyond that and the correct phrase now is keyword phrase which is a string of keywords. A keyword phrase is typed into the search engine by a user to try and find a specific website and the goal of the website is to have its website pop up close to the top of the SERPs (search engine results pages) while it is the search engines goal to display the most relevant websites near the top of the SERPs that match the keyword phrase used.