Briefly explain what are jа vascript librairies

In the spirit of clear definitions:

jа vascript is a scripting language used by front end developers (people who build parts of a website or web app that users see on their screen) to implement and manage dynamic content. There are other scripting languages out there, including Python, but JS is the most commonly used.

Therefore, jа vascript libraries are collections of pre-written code snippets that can be used (and reused) to perform common jа vascript functions.