Orbital overlap in the context of "Conjugation (organic chemistry)"

In physical organic chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases stability. It is conventionally represented as having alternating single and multiple bonds. Lone pairs, radicals or carbenium ions may be part of the system, which may be cyclic, acyclic, linear or mixed. The term "conjugated" was coined in 1899 by the German chemist Johannes Thiele.

Conjugation is the overlap of one p-orbital with another across an adjacent σ bond. (In transition metals, d-orbitals can be involved.)