The term "all-time high" (ATH) refers to the highest price an asset (stock, currency) has ever reached on an exchange. In relation to cryptocurrencies, this means that the price of a certain cryptocurrency has broken all its past records and is trading at the highest price it has ever achieved.
Exactly the opposite of the ATH would be the ATL. The All Time Low (ATL) stands for the lowest price ever recorded for a quotation.
