resonance integral, Hrs 

https://doi.org/10.1351/goldbook.R05337
In Hückel molecular orbital theory, the integral over space of the type ψr H^ ψs dτ where H^ is the hamiltonian operator and ψr and ψs are different wavefunctions.
Source:
Green Book, 2nd ed., p. 17 [Terms] [Book]