In the equation Rate = ZAB.e^-Ea/RT, what does ZAB mean?

Based on collision theory, the rate of a chemical reaction can be given as ZAB.e^-Ea/RT.

ZAB represents the collision frequency of reactants, A and B

• Reactions occur when two reactant molecules effectively collide, each having minimum energy and correct orientation.
• In the reaction A + B → ABThe rate of the reaction is equal to the number of active collisions. So the rate of reaction can be written as

  ZAB e^-Ea/RT

  Ea: is the activation energy (J/mol)