There are many definitions of keywords. Let me share the one that matters for SEO.
Keywords are single words or whole phrases of a particular SEO importance for a given page or website.
For example, if I’m writing an article about choosing the best gardening equipment, my main keyword could be “gardening equipment“. It is the keyword I want to rank for because I want people to find this article when they input “gardening equipment” into Google.
Another example is this very list. The main keyword here is SEO glossary. I want people to find this post by putting “SEO glossary” into Google