burn-in
1 of 2noun
ˈbərn-ˌin 
: the continuous operation of a device (such as a computer) as a test for defects or failure prior to putting it to use
burn in
2 of 2verb
burned in or burnt in; burning in; burns in
transitive verb
: to increase the density of (portions of a photographic print) during enlarging by giving extra exposure
Word History
First Known Use
Noun
1966, in the meaning defined above
Verb
circa 1939, in the meaning defined above