Carbon undergoes three types of hybridisations:
(i) sp³ in saturated compounds,
(ii) sp² in all unsaturated compounds containing a double bond,
(iii) sp in all unsaturated compounds containing a triple bond.

Cyclic compounds whose rings are made up of only one kind of atoms i.e. carbon atoms are called homocyclic or carbocyclic compounds.

Organic compounds containing one or more fused or isolated benzene rings and their functionalised derivatives are called aromatic compounds or benzenoids.

Cyclic compounds containing one or more hetero atoms (usually O, N, S etc.) are called heterocyclic compounds.