Typically, satellites have a roughly sinusoidal ground track. A satellite with an orbital inclination between zero and ninety degrees is said to be in what is called a "direct" or "prograde orbit", meaning that it orbits in the same direction as the planet's rotation. A satellite with an orbital inclination between 90° and 180° (or, equivalently, between 0° and −90°) is said to be in a "retrograde orbit". (Direct orbits are by far the most common for artificial satellites, as the initial velocity imparted by the Earth's rotation at launch reduces the delta-v needed to achieve orbit.)