What is the meaning of Piątka?

five (digit or figure)

five (a set or group with five elements)

something assigned the number five: bus line, road, candidate on a ballot, etc.

high five

A (the letter grade assigned) [with z (+ genitive) ‘in what subject’]

goal area (area of the pitch, extending six yards from the goal, from which a goal kick is taken)

Source: wiktionary.org