What is this type of word called?

Words that have the same spelling, but are pronounced different and mean different things.
Example:
W – I – N – D
It would either mean “wind” as in the movement of air, or “wind” as in winding up a clock or some mechanical device.

W – O – U – N – D
It would either mean “wound” as in “wind-ed” [second meaning of wind above]; or “wound” as in a flesh wound, scar, etc.