A rotation of the tape head away from perpendicular to the direction of tape/head travel.

The magnetic record and reproduce heads must be aligned to a standard angle in relation to the direction of tape and head travel. Stationary or fixed head systems with longitudinal recording paths are usually oriented with the head gap perpendicular to the direction of tape travel. In rotary head systems, the azimuth angle is relative to the combined angle of the heads passing across the moving tape.

Azimuth Error

If a head slopes away from the desired angle a loss of signal will occur. The loss is greatest at shorter wavelengths. 

Azimuth Recording

By taking advantage of azimuth error, a number of video and other rotary-head tape formats have been developed with one or more pairs of rotating heads which have opposing or complementary azimuth angles, thereby enabling the recording of adjacent tracks very closely, or even overwriting the edge of the preceding track in order to increase density.