This is the 2013th most frequent Polish word.
grup
In Polish, "grup" is not a standard word; it might be a misspelling or abbreviation.
The word 'grup' is used here to indicate the plural form of 'group', referring to sets of people learning together.
Oni zawsze uczą się w małych grupach.
They always learn in small groups.
The word 'grupa' is singular, describing one collective unit participating in the trip.
Nasza grupa idzie dziś na wycieczkę.
Our group is going on a trip today.
The plural form 'grupy' suggests dividing people into multiple collections based on interests.