least recently used
(operating systems) (LRU) A rule used in a paging system which selects a page to be paged out if it has been used (read or written) less recently than any other page. The same rule may also be used in a cache to select which cache entry to flush.
This rule is based on temporal locality - the observation that, in general, the page (or cache entry) which has not been accessed for longest is least likely to be accessed in the near future.