Answer
An angular frame is a representation of an object’s orientation in 3D space. It is commonly described using Euler angles or a quaternion. Please see http://en.wikipedia.org/wiki/Euler_angles and http://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation
An angular frame does not describe the 3D location of an object, only its rotation relative to a reference. The reference rotation for a 6-axis angular frame is flat and level—that is, the vertical axis of the object is aligned with up/down. The reference rotation for a 9-axis angular frame is flat, level, and north: the vertical axis of the object is aligned up/down, and the forward axis of the object is aligned north/south.