Coil: the coil, which is also known as the head, loop, or antenna, is the metal-sensing part of a detector. A metal detector coil is composed of wire coils in a circular or elliptical plastic housing. A detector may have one or more coils acting as both transmitter(s) and receiver(s), or it may have coils dedicated specifically to either transmitting or receiving.
Coin Shooting: a slang term for coin hunting, or going detecting specifically in search of coins.
Concentric Coil: concentric means "having a common center." Concentric search coils feature circular transmit and receive windings of unequal diameters that are aligned on a common center, producing a cone-shaped search matrix. If the wire coils/windings of a concentric coil are on the same plane, it's referred to as coplanar concentric.
Electromagnetic Field: an electromagnetic field is an invisible matrix created by electrically charged objects. In metal detectors, the electrical current moving through the transmitter coil of the search head produces an electromagnetic field, and this field extends to a depth perpendicular to the size of the coil. When the field encounters metals, they generate their own fields, which can be measured by a metal detector's receiver coil.
Elliptical Coil: an ellipse is an extended oval shape resembling a flattened circle. A search coil in this shape is called an elliptical coil. Elliptical metal detector coils can be either concentric or widescan.
Ground Balance: soil often contains ground minerals, magnetic material composed of ferric oxide and other metals. These iron-bearing materials cause loss of depth in a metal detector. Ground balance is the ability to manually or electronically ignore or neutralize these signals. This is sometimes called ground tracking or ground reject.