What is heat?

Heat is a form of energy associated with the vibration of atoms and molecules.
Such vibrations can be caused by exposure of such particles to that part of the electromagnetic radiation spectrum generally termed "infra-red" which lies between "visible light" and "micro-waves". Heat energy can also be transmitted by contact between adjacent particles (conduction) as a domino effect, or re-transmitted as infra-red.

So heat is just another form of light?

Very very simplistically.

Heat is kinetic energy. The transfer of kinetic energy as heat is through conduction, convection, or radiation.

The energy, as heat, can be considered as kinetic as a hot particles (atom, electron, or ion) has an associated velocity (on a quantum level) as this particle interacts with other particles (collisions) some of that kinetic energy is transferred (conduction).

If these particles are easily able to move (fluids) that kinetic energy moves with the fluid (conduction).

If the energy difference between particles is sufficient the energy transmission can be electromagnetic (radiation). Kinetic energy transmission by this method can be over large distances without intermediate media (matter).

Rap

No. Although "heat" and "light" are both associated with electromagnetic radiation (of differing wavelengths) the two forms of energy are considered to be distinct because of our (human) different experiences of them, and because of their differing ranges of effects. Note that logically speaking "similiarity" and "difference" are based on judgments of functionality.