A covalent relationship where two electron pairs are shared between two atoms.
A covalent relationship by which two electron sets (instead of the usual one) are provided between two atoms; typical between carbon atoms and carbon, air or nitrogen atoms, but many kinds tend to be understood.
a covalent relationship involving the merging of orbitals of two (or three) electrons for each of the two connected atoms, therefore fulfilling two (or three) units of valence for each for the bonded atoms. Whenever two carbon atoms tend to be hence bonded, the relationship (as well as the ingredient) tend to be reported to be unsaturated.
a covalent bond by which two sets of electrons are provided between two atoms