it is the process of intermixing of the orbitals of slightly different energiesso as to redistributetheir energies resulting in the formation of new set of orbitals of equivalent energies and shape.
sp:In this one s and one P orbital mix and form two equivalent sp hybrid orbital.This hybris involves the overlap between the two carbon atoms forming a ? bond and two additional ? bonds
formed by p
sp2:In sp2 hybridisation the 2s orbital is mixed with only two of the three available 2p orbitals.the two carbon atoms form a ? bond by overlapping two sp2 orbitals and each carbon atom forms two covalent bonds with hydrogen by ssp2 overlap all with 120° angles. The ? bond between the carbon atoms perpendicular to the molecular plane is formed by 2p2p overlap
sp3:In this the one s orbital "mixes" with the three p orbitals to form four sp3 hybrids.It involves four sigma bonds.
sp3d:In this one s orbital mixes with three p orbitals and one d orbital .In this three orbitals point towards the corner of a an equilateral traingle while the other two are perpendicular to the plane of the triangle.
sp3d2:In this three p one s and two d orbitals overlap , and adopt octahedral hybridisation.
sigma bond:A sigma bond is formed by end to end filled atomic orbitals along the internuclear axis.
pi bond:A pi bond is formed by the sideways overlap of two half filled p-orbitals.