Green Check Mark.
A check mark that displays with a white outlined appearance. Shows on most platforms with a bright green rounded rectangle or circle surrounding it.
Android previously displayed this as an outlined blue check mark / blue tick.
This emoji is not supported in Twitter names, possibly in an attempt to minimize confusion with a verified checkmark.
Check Mark Button was approved as part of Unicode 6.0 in 2010 under the name “White Heavy Check Mark” and added to Emoji 1.0 in 2015.