A Highly Elliptical Orbit (HEO) is characterized by a large difference between its closest approach to Earth (perigee) and its farthest point (apogee). The most well-known HEO is the Molniya orbit, with a 12-hour period and apogee over the Northern Hemisphere, providing extended coverage of high-latitude regions that geostationary satellites cannot effectively serve.
HEOs are used for specialized communications, early-warning missile detection, and scientific missions. A satellite in a HEO spends most of its orbital period near apogee, where it moves slowly, effectively hovering over the target region for hours at a time before swinging rapidly through perigee.