RxJS
In plain terms
A library for reactive programming using observable streams.
Going deeper
RxJS represents asynchronous events as observable streams you can transform, combine, and subscribe to with rich operators. It tames complex async flows.
Under the hood
Powerful but with a steep learning curve; central to Angular and complex event handling.
Examples
Angular, complex async UIs, event handling, debouncing, websocket streams.
Think of it like...
Like plumbing that lets you filter, merge, and reshape flowing streams of events.