Lagrange point
The five places are called L1, L2, L3, L4 and L5.  The first three (L1, L2, L3) are called metastable because if a satellite gets a bit out of place, it will fall away from that point, and not come back without using fuel.  L4 and L5 are considered stable - if a satellite gets a bit out of place, it will be pulled back into place by the gravity and centripetal forces, and oscillate around the Lagrange point. This can result in very wide swings around L4 and L5, sometimes called by such names as "tadpole" and "horseshoe" orbits.