He/she probably means grammatical case declension for subjects, objects, possessives and whatnot. _Der_ Hund beißt _den_ Mann. _Der_ Mann gibt _dem_ Taxifahrer

He/she probably means grammatical case declension for subjects, objects, possessives and whatnot. _Der_ Hund beißt _den_ Mann. _Der_ Mann gibt _dem_ Taxifahrer _das_ Geld. German has four cases, Polish seven(?), Russian six(?). In English it's mostly gone, but we occasionally have to go to the effort of distinguishing between subject and object (I/me, he/him, she/her).