Using VSEPR theory, what is the molecular geometry of $\mathrm{NH_3}$ (three bond pairs and one lone pair on N)?

The electron-pair geometry around N is tetrahedral (four electron domains). The lone pair occupies one of those positions but is invisible when we describe the molecular shape. Looking at where the three H atoms actually sit relative to N, the molecule is trigonal pyramidal. The bond angle is about $107°$, slightly less than tetrahedral because the lone pair compresses the H–N–H angles.