Excitation is the amount of energy (energy in a general sense, not energy as defined in physics) that something or someone has. In physics there is a specific technical definition for energy level which is why the word excitation has been chosen for the general case.
In the physical world temperature is indicative of the level of excitation.
At higher levels of excitation processes usually proceed faster.
to add: excitation in people, comparison to energy in people and physical systems