What are hybrid orbitals?

Hybrid Orbitals: are used to describe the orbitals in covalently bonded atoms sp, sp2, sp3

You can find the hybridization by adding the number of bonded atoms and the number of lone pairs.

For example in BF3. The central atom (B) is bonded to three atoms. So the hybridization is sp2

In NH3, the central atom (N) is bonded to three atoms and has one lone pair. The hybridization is sp3