Blood-alcohol level was the amount of alcohol in one's blood, as a method for measuring intoxication.
In 2151, Trip Tucker coerced Malcolm Reed into sharing bourbon with him while stranded in Enterprise NX-01's Shuttlepod 1, mocking Reed's assertion that he didn't drink on duty by asking him if he was afraid his autopsy would show a blood-alcohol level too high to pilot a shuttle. (ENT: "Shuttlepod One")