A circle is divided into 360° (angular segments) around the circumference and each degree is further divided into 60 minutes (smaller angular segments). A minute of arc is a unit of angular measurement equal to 1/60 of one degree. As one degree is 1/360 of a circle, this results in one minute of arc equal to 1/21,600 minutes of a circle.
This unit of measure is important to bearings since some designs (i.e. tapered roller) specify maximum allowable misalignment of 3 minutes.