2.4GHz: only 3 non-overlapping channels (1, 6, 11). 5GHz: many non-overlapping channels, shorter range. 6GHz (Wi-Fi 6E): even more channels, best for dense environments.
2.4GHz has longer range but more interference (microwaves, Bluetooth, neighboring APs all share 3 channels). 5GHz has shorter range but 24+ non-overlapping channels — better for dense deployments. Use 5GHz for corporate, 2.4GHz for range extension.