A specific type of val which defines an equal-temperament, which is a closed tuning system.
The name was coined by Paul Erlich -- primarily to refer to the process of "breeding" different ET species together (each represented by a breed, because it is one) to create "cross-breeds", which are the multidimensional tuning systems like meantone, and secondarily to honor the work of Graham Breed, who initiated computer algorithms which calculate tunings in this way.
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