pi
bond is an electron
pair "bond in which the parallel p orbitals share an electron pair occuping
the space above an below the line joining the atoms."
(S.S. Zumdahl, Chemistry 19892)
sp2 hybridization
of a C atom results in 1 pi bond of ethene (left),
sp hybridization of a C
atom results in 2 pi bonds of ethyne (middle, right).