Strike is the trend of a horizontal line drawn on an inclined plane (e.g. a dipping bed). It sits at right angles to the line of steepest descent, the dip of a bed and is not defined for a horizontal plane.
Fracture and fault data are often presented as strike frequency plots, see figure on the left for example where fractures are coloured in blue.
WHITTEN, D.G. and BROOKS, J. R. V. 1972. A Dictionary of Geology, Penguin Books, Hardmondsworth, p495.