This is the 43rd most frequent German word.
seine
"Seine" is the German possessive pronoun meaning "his" or "its."
The word 'seine' is a possessive pronoun modifying 'Hausaufgaben' (homework), indicating that the homework belongs to 'him' (the subject 'Er').
Er hat seine Hausaufgaben gemacht.
He did his homework.
The word 'seinen' is the dative case possessive pronoun modifying 'Spielzeugen' (toys), showing possession by someone referenced earlier.
Die Katze spielt mit seinen Spielzeugen.
The cat plays with his toys.
The word 'seine' is a possessive pronoun preceding 'Jacke' (jacket), implying that the jacket belongs to a referenced male (contextually understood).