Orbit
From Kerbal Space Program Wiki
A spacecraft in orbit around Moho.
An orbit is an elliptical path around a celestial body. The point on an orbit which is closest to the orbited body is called the periapsis; the furthest point is the apoapsis.
An orbit is considered "stable" if all points in the orbit are above the terrain and atmosphere of the orbited body. A spacecraft in such an orbit will not lose velocity due to atmospheric drag or collisions with terrain.
To achieve orbit, a spacecraft must reach a sufficient altitude and orbital velocity. During ascent, a gravity turn helps to achieve both of these goals in a fuel-efficient way.
