Can someone explain me "Events" in simple words

Answer 1

A thing that happens on doing something particular.
Like,
Pressing a key on keyboard,
Pressing a button on mouse,
etc.

Answer 2

like real life
you are told what to do when things happen
on traffic light is red. stop
on doorbell rings: go to door
on cat is hungry: feed.

now
on window.load function() {
do sth
}

Answer 3

Thank you for guiding me