Cache replacement policies are strategies used to determine which data to remove from a cache when it becomes full. These policies aim to optimize performance by keeping the most relevant or frequently accessed data available for quick retrieval. Common policies include Least Recently Used (LRU), which removes the least recently accessed data, and First-In-First-Out (FIFO), which removes the oldest data first. Choosing the right cache replacement policy can significantly impact system efficiency. For example, Least Frequently Used (LFU) targets data that is rarely accessed, while Random Replacement removes a random item. Each policy has its advantages and is suited for different types of workloads.