What is Dead Drift?

Answer 1

A "dead drift" is achieved when the fly is presented in such a manner that it floats motionlessly in perfect tandem with the current, thus creating the illusion of an insect drifting in the water. This is considered by many to be the optimal means of presenting a fly pattern to hungry fish as it mimics aquatic insect life which is their primary source of food.

The opposite of "dead drift" is "drag" which happens when the fly pattern moves unnaturally against the current (often causing a wake). This is unattractive to fish and usually does not elicit a strike.