Wikipedia
A frentera is a part of some halters and bridles, usually on a horse. It is a cord, strap, or chain on the face of the horse that is attached to the crownpiece or browband and runs down the horse's face to the noseband or bit rings. A frentera can be split at the top to pass on either side of the forelock, or on either side of the ears. In the latter case, the frentera usually substitutes for a browband. A frentera can also be split at the bottom into two or more parts to support and stabilize a heavy noseband or bit.
The known history of the frentera dates back to Ancient Greece, possibly earlier, and the frentera is in use today in Europe, Asia, Australia, and South America. When it includes a disk or sheet of metal, often silver, it is known in English as a testera ( Spanish loanword), chamfron ( French loanword), or faceplate.
Equipment with a similar purpose of stabilizing a bit or noseband include the forelock hanger (North America), bit lifter (Australia), and cheekers (Australia). The frentera is not to be confused with a similar appearing piece of tack, the overcheck.