Cache refers to storing data for quicker access at a later time. The word can be used as a noun (e.g. "the cache of data") or a verb (e.g. "cache the data").
Video data can be cached at a number of points in the delivery pipeline. CDNs cache video data in edge servers closer to users. Web browsers cache the results of requests for video data so that later requests for the same data can pull from the browser's memory.