Keywords versus search terms
A keyword is what you target; a search term is what a real person actually searched. With broad and phrase match, the two can diverge sharply. The search terms report is where that gap becomes visible, and where you catch the off-intent traffic quietly draining budget.
What to do with it
Review it regularly and add irrelevant queries as negative keywords, promote high-intent terms into their own tightly matched ad groups, and use it to sanity-check what a broad match keyword is really matching. Note that Google withholds some low-volume terms for privacy, so it is thorough but not complete.
Common questions
What is the difference between keywords and search terms?
Keywords are what you bid on. Search terms are the exact queries that triggered your ad. Broad and phrase match mean a single keyword can match many different search terms, some off-intent.
Why does the search terms report not show every query?
Google hides some terms that too few people searched, to protect user privacy, so the report covers most but not all of your traffic.