1. Derived from German ("five liter day"), a phrase describing a the plan to drink at least 5 liters (1.32 gallons / 176 fl oz) of beer on a given day, which is widely considered the perfect amount.

2. May also be used as a verb
1. Kevin: "Guys! 5-Liter-Tag today, ja?"
Everyone: "ok" *starts drinking*

2. Manuel: "Dude, i'm totally gonna 5-liter-tag today, bro!"
Victor: "Oh, sweet. It's lit!"
by oddsmeister March 1, 2019
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