Tundra orbits are named for the tundra biome, a cold climate found in the far North where the subsoil is perpetually frozen, the growing seasons are short and the landscape is dominated by small, hardy plants such as low shrubs, mosses and lichens. Tundra orbit satellites follow an usual path that allows them to communicate with people living in Tundra regions. Rather than orbiting the Earth at a set distance, tundra orbit satellites follow highly elliptical orbits, constantly moving away from the earth, then back toward it. Tundra satellites are currently used by Sirius Satellite Radio to provide service to the Northern Reaches of North America.
Tundra orbit satellites are synced up to the earth's rotation; each satellite makes one rotation around the earth per day. The satellite does not stay in precisely the same spot relative to the ground, but does track the same ground area every day without drifting. This allows tundra orbit satellites to be used for ground-based communication.
Geostationary satellites (satellites that stay above the same spot on the ground) must sit directly above the equator, which does not allow them to send transmissions to the far north. Tundra orbit satellites are designed to spend most of their time north of the equator. This allows them to transmit to remote reaches of Alaska and Northern Canada, which geosynchronous satellites can't reach.
An individual tundra satellite cannot cover an area continuously, because it periodically drifts too far south. Fortunately, a group of tundra satellites can. Sirius Satellite Radio uses three tundra satellites with overlapping orbits to transmit to the United States and Canada. When one satellite is out of range, at least one of the other two is within range to transmit. Tundra satellites could be put into orbit to cover Northern Europe and other areas far from the equator with continuous satellite transmissions.