What are Kotlin coroutines and how do they work?

Coroutines are lightweight threads for asynchronous programming. They allow writing asynchronous code in a sequential manner. Key concepts: 1) suspend functions - can be paused and resumed, 2) CoroutineScope - defines lifecycle, 3) Dispatchers - control thread execution (Main, IO, Default), 4) launch{} - fire-and-forget, 5) async{} - returns result. Example: suspend fun fetchData() { delay(1000) }. Coroutines are more efficient than threads.