MMR
Your matchmaking rating (MMR) is an individual score based on your PvP rating (an ELO-like calculation that updates every time you kill or are killed by another Hunter) and other modifiers. For example, if you don't play Hunt for a while, your score is recalculated accordingly.
Your MMR is displayed on a scale from 1 to 6 stars and can be viewed in the lobby or on the team details screen by clicking the MMR icon.
MATCH MMR
Your Match MMR is the MMR score for your entire team. Match MMR is calculated using an average of the team's individual MMR scores, with additional modifiers applied to help place smaller teams and random teams in fair matches. Match MMR is displayed in half-star increments, while individual player MMR is displayed in full-star increments.
Each star represents a range of individual MMRs. For example, one star represents an individual score range from 0-500. It follows that there may be cases when you see two teams with the same individual ratings, but different Match MMRs. This is because of a difference in the exact score behind the star rating.
ACTIVE MODIFIER
Match MMR includes calculations known as modifiers that help compensate for handicaps.
Possible modifiers include: playing solo, playing as a duo, and playing with random teammates. Each of these circumstances may modify your Match MMR more drastically, depending on which modifiers are active. Modifier severity is shown next to your Match MMR score.
Modifiers are applied to your team; they are not altered based on the other teams in the match. If there are only random duo teams in a match, for example, all teams will have the same modifiers applied.