When a girl says "heyyy", what does that mean?

That’s a really complicated question.

Usually hey just means hello, but that’s only when normal human beings say it. When a GIRL says it, it can mean a ton of things, depending on how she says it.

It could mean, hello, obviously.

It could also mean, I like you, do you like me?

It could also mean, I love you and want to marry you and have your kids and hope you never cheat on me because if you do, I’ll snap off your ♥♥♥♥♥!

It could also mean, higgs boson particle didn’t really prove anything as far as the true nature of the universe goes.

Or it could mean, blah… blah… blah…