What does it mean to take a tab?

To "take a tab" typically means to consume a small, often paper-based dose of a substance, most commonly associated with drugs like LSD, which is often distributed on small squares of paper. It can also refer to keeping a record of a financial transaction or debt, as in "taking a tab" at a bar or restaurant, where the establishment keeps track of what a customer orders until they settle the bill. Context is important, as the meaning can vary based on the situation.