A fist raised in the air that may be used as a celebratory gesture: the fist pump.
This gesture in real life is associated with protests and support of someone or something — in these meanings it is used online as well. Commonly, it is followed by emotional smiley, which expresses the attitude more vividly — for example, by?Pouting Face emoji to convey protest.
It is also often followed by friendly or neutral-looking smileys when it means support. And at last, sometimes it is used as something like the intensifier of some statement.
Raised Fist was approved as part of Unicode 6.0 in 2010 and added to Emoji 1.0 in 2015.
U+270A
✊ Raised fist