Definition of Conjugated
Conjugated molecules are those molecules that have a conjugated system present in them. A conjugated system has p-orbitals with electrons which are delocalized. This enables the overall energy of the molecule to get lowered and hence the stability is increased. The system has regions where the p orbitals tend to overlap each other and in this way, allow the pi electrons to delocalize across the p orbitals.
The conjugated molecules typically have alternative single and multiple bonds in them. The conjugated molecules may be ringed, acyclic, linear, etc.
Examples of such molecules include graphene, graphite, carbon nanotubes, etc.