Hybridisation is phenomenon of combining two atomic orbitals to give a new degenerate hybrid orbital which have same energy levels.
Hybridisation increases the stability of bond formation than unhybridised orbitals.
We can predict the shape of molecules by its hybridisation.
Hybridisation occurs during bond formation not in isolated system.
Not only half filled orbitals even fully filled orbitals can also participate in hybridization.
Example- Formation of Methane involves a combination of three p orbital of Carbon and one s orbital of Hydrogen to form hybridized orbitals and a tethrahedral geometry.