What is Ramp, flat, duplex, out-of-sequence thrust?

A flat (thrust) is a segment of a thrust that runs parallel to the bedding, usually in a weak layer; a ramp (thrust) is a segment that cuts across the bedding, typically at 20 to $30{}^{\circ}$, joining a lower flat to an upper one. A duplex (thrust) is a stack of fault-bounded slices, the horses, enclosed between a floor thrust below and a roof thrust above, each horse cut off by a ramp that joins the two. Thrusts usually form in sequence, each new one in the footwall of the previous one, closer to the foreland; an out-of-sequence thrust is one that forms or slips again behind the active front, cutting older thrusts.