Wink

[1] A wink is an informal mode of non-verbal communication usually signaling shared hidden knowledge or intent.

A wink could also be used as a somewhat humorous way to express sympathy, solidarity, and encouragement, especially when the winker is trying to put the receiver at ease in a situation where they might feel nervous or uncomfortable.

[6][7] In China and reportedly to some extent in India, winking to anyone other than family or a friend who a person wishes to have sex with may be seen as an offensive or at least an impolite gesture.

When Frederick Spencer Chapman was training Chinese guerillas in Malaya to shoot rifles, he found that a large proportion of them were unable to close only one eye at a time.

It can be used to signal an "inside" joke, a sly gesture shared between two people privately, unbeknownst to those around them, as in a social gathering.

In Netherlands and Indonesia, winking at strangers will generally be perceived as offensive or even as a sexual advance and is unlikely to be appreciated.

West African parents may wink to signal children to leave the room, especially when there is a guest, or another adult coming in.

Parents also try not to embarrass themselves in front of guests, because their children do not understand immediately when it is time to leave the room.

Dogs are said to wink as a sign of non-aggression due to the fact they see extended eye contact as a challenge for dominance.