This is the 1304th most frequent Polish word.
matki
"Matki" means "mothers" (genitive or nominative plural form) in English.
'Matki' in this context is the genitive singular form of 'matka', indicating possession.
Widziałem zdjęcie matki na ścianie.
I saw a picture of the mother on the wall.
'Matki' is used here as the genitive singular form to indicate possession or relation in an explanatory context.
Opowiedz historię matki, którą spotkałaś.
Tell the story of the mother whom you met.
In this sentence, 'matki' appears in the genitive singular form, used again to indicate possession or association with 'uczennicy'.