unsurpassed in some respect up to the present; "prices at an all-time high"; "morale at an all-time low"; "among the all-time great lefthanders
You use all-time when you are comparing all the things of a particular type that there have ever been. For example, if you say that something is the all-time best, you mean that it is the best thing of its type that there has ever been. The president's popularity nationally is at an all-time low Duane Eddy is John Peel's all-time favourite artist. used when you compare things to say that one of them is the best, worst etc that there has ever been an all-time high/low