jQuery is one of the most popular JavaScript libraries. It includes classes and functions that allow you to quickly traverse and manipulate a web page, without having to force a full-page refresh every time something changes. A minimal version is available to reduce the amount of overhead. It is actively maintained and is supported by a large variety of browsers.
If you look at the actual statistics on https://github.com/jquery/jquery, you will see that the library has almost 300 contributors, over 53,500 star ratings, and has been forked over 19,400 times (that means 19,400 other projects are using this library). In terms of the market share of all the websites surveyed, W3Techs places jQuery at over 75% as of July 2020. The next highest comparable JavaScript library is Bootstrap, which comes in at 21%.