The true dip is the steepest line that can be drawn on an inclined plane. Measured in terms of inclination (from the horizontal) and its bearing (from north), and when used in conjunction with unit length it can be considered a vector quantity. The azimuth of the dip is at right angles to the strike of a bed. In borehole image and dipmeter processing, dips are referenced to true north following correction for tool and hole orientation; this is the usual way of presenting dips.
WHITTEN, D.G. and BROOKS, J. R. V. 1972. A Dictionary of Geology, Penguin Books, Hardmondsworth, p495.