English definition of “happen”
/ˈhæpən/ verb [I]
EXIST › If an event or situation happens, it exists or starts to be done, usually by chance: Were you anywhere nearby when the accident happened? We can't let a mistake like this happen again.
RESULT › to be the result of an action, situation, or event that someone or something experiences: Did you hear what happened to Jamie last night? What happens if we can't get enough tickets?
happen to do sth › to do something by chance: If you happen to see Peter, say "hi" for me. You don't happen to know her phone number, do you?
as it happens; it so happens › something that you say in order to introduce a surprising fact: As it happens, her birthday is the day after mine.