What is hybridisation?
Covalent bonds are formed when atomic orbitals overlap. This overlap is known as hybridisation.
There are two types of orbital overlap that an organic chemist needs to be familiar with. Sigma, s, overlap occurs when there is one bonding interaction that results from the overlap of two orbitals. Pi, p, overlap occurs when two bonding interactions result from the overlap of orbitals.
In Ch3COOH, hybridisation of C of CH3 is sp3 and that of COOH is sp2.