all-time
adjective [ before noun ] uk/ˌɔːlˈtaɪm/ us/ˌɑːlˈtaɪm/
前所未有的，空前的
An all-time high, low, best, etc. is the highest, lowest, best, etc. level that has ever been.
After three years of drought, the water in the lake had reached an all-time low. 遭受三年干旱后，该湖水位达到历史最低点。