What does a wink mean?

I'm really confused about winks. It might be a bit silly, but I can't tell when someone is winking to be friendly or silly or if they are winking to be fliry and suggestive. How can you tell what a person means when they wink? some people I know wink all the time in text or chat, even if we are having a normal coversation. Someone please enlighten me! (girls' and guys' answers accepted)
What does a wink mean?
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