A collision between two molecules in which the amount of energy transferred from one to the other is large compared with kB.T, where kB is the Boltzmann constant and T the absolute temperature.
Source:
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 188 (https://doi.org/10.1351/pac199668010149)