He's a Comedian or Interested
Some people wink after making a joke or sarcastic remark.
When a guy does this, he's making the extra effort to establish a personal understanding like saying, "You get me, right?" He's likely just trying to be friendly. To know if the wink means more than just friendship, pay attention to the rest of his body language. Making eye contact and holding your gaze indicate romantic inclinations -- as does touching you.
When you're on a dating website and you get a "wink" from a guy, you really can't be sure what it means.
Maybe he'd like to get to know you better, but he's shy and unsure what to "say" in an actual message. Or, he might be the kind of guy who winks at a lot of woman and can't be bothered sending a message. If this is the case, it doesn't mean much.
It's Your Move
Whether you receive an in-person or online wink, you can choose to ignore it or acknowledge it and respond.
If you feel an attraction and are up for a bit of flirting, you might not want to just let it go.