Explain async/await in Python and when to use it.

asyncio enables concurrent I/O-bound operations in single thread. async def defines coroutine; await pauses execution until awaitable completes. Event loop manages coroutine scheduling. Use for: network requests, file I/O, database queries, web scraping. asyncio.gather() runs coroutines concurrently. aiohttp, asyncpg for async libraries. Benefits: efficient I/O (no thread overhead), simpler than callbacks. NOT for CPU-bound tasks (GIL still applies). Example: fetching multiple URLs concurrently. Pattern: async with, async for for async context managers and iterators.