It isA classic smiley, turned upside down. Implemented as a flipped version of ? Slightly Smiling Face on most platforms.
Commonly used to convey irony, sarcasm, joking, or a sense of goofiness or silliness. Its intent can be similar to the bemused Oh well! of ? Person Shrugging or the shruggie emoticon, ¯\_(ツ)_/¯.
Microsoft's design previously featured a full-toothed grin.
Upside-Down Face was approved as part of Unicode 8.0 in 2015 and added to Emoji 1.0 in 2015.
U+1F643
? Upside-down face