It’s really no different than with any other kind of energy. Heat is basically just energy that is disorganized ie distributed in a way that is too complicated for us to keep track of – like the random motion of molecules in a gas as opposed to bulk motion or pressure waves in that same gas.
With regard to electromagnetic radiation, every hot body emits a broad spectrum of disorganized electromagnetic radiation at all frequencies – not just infrared (though that is the dominant range at the temperatures we normally experience); but it is also possible to produce organized electromagnetic radiation (eg from electronic circuits and lasers) and this is not “heat” even when it is infrared (though it can be used to create heat when absorbed by a body – just as organized mechanical energy can be converted to heat by friction).