Caches have limited memory. When full, you must evict something.
LRU (Least Recently Used): Remove the item accessed longest ago. Most common. Works well for most workloads.
LFU (Least Frequently Used): Remove the item accessed least often. Good when some items are consistently hot.
TTL (Time To Live): Items expire after a fixed time. Good for data that becomes stale.
Random: Pick randomly. Surprisingly effective and simple to implement.
In interviews, default to LRU unless you have a reason for something else. Mention TTL as a secondary mechanism.