Steric Number Definition:
The Steric Number for an atom is the total number of sigma bonds formed and the number of lone pair electrons on the respective atom.
Steric Number Explained:
The steric number is an important concept covered under the VSEPR theory. The number is calculated mainly for the central atom of the compound which is then used to predict the geometry of the compound. In other words, the number indicated the total number of bonding and non-bonding electrons of the atom that is repelling each other. This repulsion causes the electron pairs to arrange themselves in a particular geometry.
See, VSEPR Theory, Trigonal Planar, Trigonal Pyramidal, Tetrahedral.
Recall, a double bond has one sigma and one pi while a triple bond has one sigma and two pi bonds.