Varnish does call it coalescing. Grace is used for a specific situation: When a previously cached object has expired, Varnish won't evict it from the cache imme

Varnish does call it coalescing. Grace is used for a specific situation: When a previously cached object has expired, Varnish won't evict it from the cache immediately, but will continue to serve the old content, while sending exactly 1 request to the background to refetch. How long an object can live after expiring is called the grace. The HTTP standard calls this behaviour "stale-while-revalidate".