This is meant to be a canonical Q&A for all the caching questions we get on meta
- What is caching?
- Where is caching employed across the network?
- Approximately how long ought it take for each cache to update?
What is caching?
Caching is the storing of dynamic data in static form for reasonable periods of time. This reduces the number of queries required to display a page. The Stack Exchange engine caches heavily in places, to minimize cross-site queries. It uses Redis to help facilitate this. There is more on how exactly SO caches here.
Where is caching employed, and approximately how long should it take for the cache to update?