I have heard this term a few times...I did a search and started reading the posts...but there are many posts...what is a mid arm quilter?? Is it just a regular sewing machine that you do FMQ'ing on?

mid arm machines have a 9 inch throat.

And a long arm has up to an 18 inch throat.

Longarms are the large quilting machines, with throats over 18", midarms are under 18".

Out of curiosoity I did a search to see what I could find. It seems like various people have different opinions. One book has domestic machines 10" throat space or less, midarm machines 15-18" throat space, and largarm machines over 18". This book skips over machines that have between 10 and 15" throats or harps. Other places I found list the numbers similiar to what has already been said.

Many people use the term longarm to encompass any size quilting only machine. They will even refer to the 9" domestic machines as a longarm if they are sitting on a frame. Mid-arm to most is any of the 9-18" machines that can be used on a machine quilting frame but are not necessarily permanently fixed onto a quilt frame like a true longarm.

Some people call the 10-15" machines short-arms & 16-18" midarms. Knowing the different machines & moddels is the only real way of determining how large the throat. Even then you will occasionally run into a machine that has been stretched or a converted industrial machine that doesn't fit in any of the short, mid, or longarm categories.