A heat pump is just like a central air-conditioner when running in COOL mode. However, during the winter months or when it is cold outside, a heat pump has a component called a reversing valve that allows it to reverse the flow of refrigerant. Instead of removing the heat and humidity from the structure and subsequently cooling it as a result, a heat pump extracts ambient heat from the outside air and moves it into the structure. There is heat in the air right down to absolute zero. However, once it gets below freezing, even the newest, most efficient, top-of-the-line heat pumps tend to struggle in terms of heating performance without some sort of backup heat.
In areas where it is almost always warm, like many parts of Florida, a heat pump with no backup heat (gas, oil, electric) is just fine. However, the farther North you go, the more likely you are to need backup heat. Electric strip heat is little more than oversized toaster coils with a fan that blows over them to circulate the heat through the building's ductwork. This will work anywhere in the country, but the farther North you go, the more expensive it is going to be to run it. In parts of the country with really cold winter climates, a heat pump matched up with a gas or oil furnace, or even a hot water boiler, is a very efficient choice, possibly even more efficient than a straight-cool central air-conditioner matched up with a furnace. This is called a hybrid or dual-fuel system.
My friend's house in the Pennsylvania has a heat pump, and it sucks at heating when it gets below forty degrees!
My new house has a heat pump and a gas furnace for maximum efficiency