What is VSEPR model, steric number?

In the VSEPR model (valence-shell electron-pair repulsion), the pairs around a central atom A repel one another and take the arrangement that keeps them farthest apart. A molecule is written $\ce{AX_nE_m}$, where $n$ is the number of atoms bonded to A (a multiple bond counts once) and $m$ the number of lone pairs of A. The steric number $n + m$ fixes the arrangement of the pairs: 2 linear, 3 trigonal planar, 4 tetrahedral, 5 trigonal bipyramidal, 6 octahedral. The shape of the molecule is the arrangement of its atoms only.