Lagrange points:
Points within the vicinity of two massive bodies (like the Earth and the Moon) where each others' respective gravities balance. There are five, labeled L1 to L5. L1, L2, & L3 lie along with the centerline among the centers of mass among the two masses; L1 is onto the inward side of the secondary, L2 is in the external side of the secondary; and L3 is in the external side of the primary. L4 & L5, the Trojan points, lie along the orbit of the secondary about the primary, sixty degrees ahead and behind of the secondary.
L1 through L3 are points of uneven equilibrium; any disturbance will move a test particle there out of the Lagrange point. L4 & L5 are points of constant equilibrium, provided that the mass of the secondary is less than approximately 1/24.96 the mass of the primary. These points are constant because centrifugal pseudoforces work against gravity to cancel out it.