In Lewis structures, the number of electron pairs shared by two atoms. In molecular orbital theory, the net number of electron pairs in bonding orbitals (calculated as half the difference between the number of electrons in bonding orbitals and the number of electrons in antibonding orbitals.

the difference between the number of bonding electrons and the number of antibonding electrons, divided by two

electron hydronium ion monoprotic acid sigma orbital

Bond order is the number of bonds between a pair of atoms. For example in nitrogen N:::N the bond order is 3, in acetylene H:C:::C:H the bond order between the two carbon atoms is 3 and the C:H bond order is 1. Bond order gives an indication to the stability of a bond.