Bucket

Think of the mail slots at a hotel. Each room has one, but the staff might drop several letters in the same slot if several guests share a name. The slot itself is a bucket; the letters inside form a chain.

buckets[3] ─→ ┌─────┐     ┌─────┐
              │ key │ ──→ │ key │ ──→ NULL
              └─────┘     └─────┘

More buckets than entries → most buckets empty, lookups fast. Fewer buckets than entries → long chains, lookups drag.