Lagrangian point

La·gran·gi·an point  (l-grnj-n)

n.

Astronomy Any of five points, stable with respect to gravitational forces and in the orbital plane of two bodies, one of which is much larger than the other. A third, smaller body placed at one of these points will remain in equilibrium with respect to the other two bodies.

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[After Comte Joseph Louis Lagrange.]

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Lagrangian point  (l-grnj-n)

A point in space where a small body with negligible mass under the gravitational influence of two large bodies will remain at rest relative to the larger ones. In a system consisting of two large bodies (such as the Sun-Earth system or the Moon-Earth system), there are five Lagrangian points (L1 through L5). Knowledge of these points is useful in deciding where to position orbiting bodies.