Caching Layer
In plain terms
A dedicated tier storing frequently-accessed data for speed.
Going deeper
A caching layer sits between the app and slower data sources to serve hot data fast and reduce load. It trades freshness for performance.
Under the hood
Cache invalidation and consistency are the hard parts; layers include in-memory, distributed (Redis), and CDN.
Examples
Redis/Memcached, CDN, database query cache, API response caching.
Think of it like...
Like a front-desk shelf of popular items so staff don't fetch from the warehouse each time.