Bond order ($b=(N_b-N_a)/2$)

In the elementary molecular orbital theory count, bond order is half the excess of Electrons in bonding molecular orbitals over those in antibonding molecular orbitals. Thus adding one Electron to a bonding molecular orbital raises $b$ by $1/2$, while adding one to an antibonding molecular orbital lowers it by $1/2$. The configurations drawn above give $1$, $1/2$, and $0$. This count summarizes net covalent bond occupancy; it is neither a measured energy nor a universal test for every kind of binding. See Chemistry 2e, 8.4: molecular orbital bond order.