These systems are called “mini-splits” because they are miniature versions of the heat pumps installed from the 1970s to the 1990s. And they are “splits” because they rely on two pieces of equipment which are split from each other—connected only by two thin pipes and an electric cable.
The outdoor unit collects and compresses the heat. The unit then transfers the heat to a high-pressure gas or liquid that runs through a pipe into the home. There it is distributed by an air handler which is just like the radiator in a car. Air is pulled through the radiator by a fan, absorbing the heat from the superheated gas or liquid without mixing with it.
For space heating in almost every climate, heat pumps are an energy-efficient choice of electric heating.
In summer, the mini-split works in reverse by taking heat out of the air in your home and moving it to the outdoor unit where it is transferred to outdoor air. That’s air conditioning!
Another feature of a heat pump is that it can remove moisture from air. In summer, removing moisture from the air inside your home and lowering the relative humidity can make your home more comfortable, even if the temperature of the air inside your home is a bit higher than your usual set point temperature (e.g., 68-70F). Most air conditioners remove moisture from the air even as they cool the air. However, in the spring and fall, you may not need to cool the air, but it still feels a bit “sticky” or “clammy.” A heat pump which does not heat or cool the air, but rather is designed to remove moisture, may be helpful. You might want to consider a dehumidifier either for your whole house or specific rooms, for example a clammy basement.