wait how does that work? because you're borrowing the heat from somewhere else?

Yes, that’s why it is called a “heat pump”. It leverages the temperature change from compression expansion of a refrigerant that cycles in a loop to gather heat from one environment and deliver it to another, so that (within limits of temperature on both ends) it can heat or cool a targeted space, doing the opposite elsewhere—outside (or in the ground, for a geothermal system), when we are talking about the first space as a building, generally.