A cuff is the very end of a long sleeve or the rolled bottom of your jeans. You might prefer to wear a cuff on the bottom of your pants in order to show off your striped socks.
One kind of cuff is at the end of your sleeve or trouser leg, and another is a type of jewelry you might wear around your wrist, like a wide gold cuff. You can also use the word cuff as shorthand for handcuff, the silver kind that police officers put on suspects' wrists during an arrest. The mid-fourteenth century version was cuffe, and it meant "mitten or glove," from the Medieval Latin cuffia, or "head covering.