What are Kotlin coroutines and how do they differ from threads?

Coroutines are lightweight concurrency primitives that run on threads but do not block them.

Threads are OS-level constructs, expensive to create and manage. Coroutines are user-space constructs managed by Kotlin runtime. They suspend execution instead of blocking threads, enabling millions of coroutines on few threads. Dispatchers control execution context (Main, IO, Default). Structured concurrency ensures lifecycle-bound execution.