Definition of all-time adjective from the Oxford Advanced American Dictionary

 

all-time

 adjective
adjective
 
[only before noun]
 
jump to other results
(used when you are comparing things or saying how good or bad something is) of any time one of the all-time great players my all-time favorite song Unemployment reached an all-time record of 14.5 million. Profits are at an all-time high/low.
See the Oxford Advanced Learner's Dictionary entry: all-time