A cone was a three-dimensional geometric shape.
The object of the Ktarian game was to make a disc go into a cone. In 2368, Etana Jol instructed William T. Riker to do so while playing the game. (TNG: "The Game")
In 2374, the EMH Mark II described a thrombic modulator to The Doctor as a "cone-shaped device." (VOY: "Message in a Bottle")