The term "apple polisher" is a slang expression that refers to someone who tries to win favor from a person in authority, often a teacher or boss, by giving gifts or acting extra nice. It essentially means someone who flatters or curries favor with people of influence, often in an attempt to get special treatment. The image evoked is of someone polishing an apple to give to an authority figure as a gift or bribe. So in short, an "apple polisher" is a person who engages in this kind of flattering or gift-giving behavior to gain advantage or approval.