It stands for integrated dual feed, it has the similar effect as a walking foot except you have that action of the top and bottom feeding the fabric evenly as part of the machine itself as opposed to having it only when you have the walking foot on. for me as a reasonably new sewer it means alot less to think about and smoother even stiches with multiple layers. You don't need a walking foot for quilting and Iused the - i think its narrow edge foot - makes stich in the ditch heaps easier. I think other brands say they have something similar but so far as i know pfaff has it as one of their main features