(Pieces of) ice placed in a drink, or into which a bottle or other container is placed, to cool the contents.

a block of ice; (in modern use) spec. a small block of ice formed in a mould in a freezer or freezing compartment and used to chill drinks.

In figurative or allusive uses. slang (originally U.S.). In plural. Cubed ice for use in an (alcoholic) drink. Frequently in on the rocks (see…