Definition of "On" :

adjective: in operation or operational

"Left the oven on."

adjective: (of events) planned or scheduled

"The picnic is on, rain or shine."

adverb: with a forward motion

"We drove along admiring the view."

adverb: indicates continuity or persistence or concentration

"His spirit lives on."

adverb: in a state required for something to function or be effective

"Turn the lights on."