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.