This is the 7184th most frequent Japanese word.
一杯
"一杯" (いっぱい) can mean "one cup/glass," "full," or "a lot."
Here, "一杯" is used to denote a single cup of liquid, typically representing a unit or measure.
私は一杯のコーヒーを飲んだ。
I drank a cup of coffee.
In this usage, "一杯" expresses a state of being full or having many items or tasks.
彼は仕事が一杯あると言っていた。
He said he has a lot of work.
This context uses "一杯" colloquially to refer to having a drink—often alcoholic—in social settings.