Radial Male & Female
The cross section of the O-ring can be measured in both the axial and radial direction. A radial seal uses the radial cross section of the O-ring to seal around a piston. There are two variations of a radial seal: a male and a female design. The male design places the groove and O-ring on the piston. This may also be called a piston seal. A variation of this is the female design, which places the groove inside the bore. This may also be called a rod seal.
Radial seals will see movement during installation, however once in place, the O-ring is considered static.