C++ is a programming language. Boost is a very popular set of libraries that contain utilities like different popular data structures or things like that but it doesn't automatically come with C++. When you ask a question about "what's the easiest way to do X in C++?" Often someone will answer by linking to boost.

But boost is also giant, and you don't necessarily want to include such a huge dependency into you project just for one simple task you were asking about so it's kind of not always a great answer despite being extremely common.

JavaScript is also a programming language usually meant for running in web browsers. It's got a lot of platform-dependent quirks: some things work in chrome but not firefox or has some weird edge case in IE.. To smooth out these platform dependent quirks (and also add some really nice utilities and syntax helpers) theres a library for javascript called J-query. It too is pretty big so if you have a small JavaScript project and want to do one simple thing you don't necessarily want to include all of jquery but if you ask online"how do i do X in JS" it was so common for someone to suggest using Jquery that it became a meme to do so among (especially web) developers.