Hot is the opposite of cold. This could mean a hot day in July, a baseball team on a hot streak, or a hot bikini model.
Most meanings of hot have to do with heat: what makes us sweat. A stove can be red hot. Spicy food is hot, and newspapers used to be "hot off the presses" because the printing process actually warmed the paper. New things are often referred to as hot — like a hot new band. Stolen property is also called hot because you can't hold onto it too long or it will burn you — though perhaps not in the usual way.