Library:
React is the Javascript library which uses the virtual DOM (clone of a real DOM) and it is used to create more attractive user Interfaces.

What is mean by Virtual DOM??
Virtual DOM is a light weight copy of a actual DOM while actual DOM is slow but manipulation using virtual DOM is fast whenever there is a change in the state of any element, a new Virtual DOM tree is created. This new Virtual DOM tree is then compared with the previous Virtual DOM tree and make a note of the changes.

User Interfaces:
Helps to build user Interfaces using bootstrap,material UI,Tailwind

Components:
In react each and every elements are reusable and we easily reuse those by using these by simply importing and exporting inside our components

Conclusion
when comparing to other frontend frameworks like Angular,vue,svelte.React is much easier to learn other than that React was preferred over by many companies,React community is the largest one