1. The effect of the velocity of fluid flow upon the velocity (relative to a fixed external point) of an object moving within the fluid; the vector difference between the velocity of the object relative to the fluid and its velocity relative to the fixed reference. In air navigation, drift is often couched in terms of angular difference between heading and course, and thus can be produced only by a crosswind; when the wind velocity is parallel to the heading of the aircraft (direct headwind or tailwind), the drift is considered to be zero. The calculation of the drift (leeway) effects upon an ocean-going vessel is complicated by having to consider the combined effects of two fluids in motion. 2. “In geology, materials in transport by ice; deposits made by glacial ice on land, in the sea, and in bodies of meltwater. ” (Glossary of Arctic and Subarctic Terms, 1955. ) 3. The speed of an ocean current. In publications for the mariner, drifts are usually given in miles per day or in knots. 4. See snowdrift. 5. The horizontal track of an object, for example, clouds, caused by the wind or fluid motion. Also refers to a shift in the calibration of a satellite sensor or change in the orbital track of a satellite.