What is garbage collection in C#?

The garbage collector (GC) is the CLR's automatic memory management system. It periodically identifies objects on the heap that are no longer reachable (no live references) and reclaims their memory — freeing developers from manual memory management (no free() like in C). The .NET GC uses a generational model with three generations: Gen 0: newly allocated, short-lived objects — collected most frequently, very fast. Gen 1: objects that survived Gen 0 collection — a buffer between Gen 0 and Gen 2. Gen 2: long-lived objects — collected infrequently, most expensive. Large Object Heap (LOH): objects ≥ 85KB, always Gen 2. GC pauses your application during collection (though .NET 5+ GC is increasingly concurrent). Tips: avoid unnecessary allocations, use Span<T> and ArrayPool<T> for hot paths, implement IDisposable for unmanaged resources.