Lagrangian point (Earth-5875)

Lagrangian points, also known as Lagrange points, L-points, or libration points, are positions in an orbital configuration of two large bodies, where a small object affected only by the gravitational forces from the two larger objects, will maintain its position relative to them. The concept was discovered in 1772 by French mathematician Joseph-Louis Lagrange, which he studied extensively in the three-body problem.

The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the centripetal force required to orbit with them. There are five such points, labeled L1 to L5, all in the orbital plane of the two large bodies. The first three are on the line connecting the two large bodies; the last two, L4 and L5, each form an equilateral triangle with the two large bodies. The two latter points are stable, which implies that objects can orbit around them in a rotating coordinate system tied to the two large bodies.

Source

 * Lagrange point on Wikipedia