I have noticed a number of folks who are using the words "mastermind group" and "group coaching" as if they were one and the same. They are not.
The term "mastermind group" apparently originates with Napoleon Hill (in Think and Grow Rich) and refers to the coming together of a group of individuals for the express purpose of developing and exchanging ideas. Behind it is the notion that two heads, three heads, etc. are better than one when focusing on a common purpose/problem. The idea quickly caught on in business .
The term "group coaching" refers to a process of coaching multiple individuals simultaneously in a common time frame. It is an extension of individual coaching while retaining most of the precepts. The most obvious, and perhaps only, commonality is the presence of more than two persons in the process.
In both, the group size is optimally around 10. Both may include a moderator although the mastermind does not need one to function, while group coaching certainly does. The group nature is significant in both processes for the same reasons: the ability of multiple intelligences to focus on a single idea and the mutual empathy and support of other members.
The differences are multiple and critical. In the mastermind group, the primary focus is on problem solving, idea generation, discussion of the ideas, analysis of the problems, discussion of the solutions, and so on. The interactions are non-hierarchical and free flowing.
In group coaching, the primary focus is on the individuals who comprise the group and that focus is more than problem solving and idea generation (although it surely may include those). The interactions are hierarchical (the coach is the moderator, leader, and input generator) and moderated and directed.
More often than not anymore, I see folks putting together what really is group coaching and calling it a mastermind group. Each of the two groupings serves a specific purpose and both are very valuable. Be very clear which you feel you need and why, and be very sure that the program you are looking at is what you think it is!
