A gesture showing the index finger and thumb touching to make an open circle.
The meanings in which it is used are obvious — it is a recognized sign of approval of some offering, agreeing with some statement, or just saying that the user is absolutely fine as the answer to the questions like "How are you?".
This can also be used as a symbol of White Supremacy, depending on context.
OK Hand was approved as part of Unicode 6.0 in 2010 under the name “OK Hand Sign” and added to Emoji 1.0 in 2015.
U+1F44C
? Ok hand sign