I was recently writing and found out that i couldn't use just one word to describe 4 people. For Example there is "Duo" for two people and "Trio" for three people. What terms can be used to describe more numbers?
You can use foursome to describe a group of four people, although the term is normally used in the context of a social gathering. The group does not necessarily have to be mixed-sex.
A group of four people meeting for a social activity, such as playing a game or having a meal:
Why don't we invite Caroline and Mark and make up a foursome?