Azimuth is the angle a line makes with a meridian, measured clockwise from north. Thus the azimuth of due north is 0º, due east is 90º, due south is 180º, and due west is 270º. You can instruct several Mapping Toolbox™ functions to compute azimuths for any pair of point locations, either along rhumb lines or along great circles. These will have different results except along cardinal directions. For great circles, the result is the azimuth at the initial point of the pair defining a great circle path. This is because great circle azimuths other than 0º, 90º, 180º, and 270º do not remain constant. Azimuths for rhumb lines are constant along their entire path (by definition).
For rhumb lines, computing an azimuth backward (from the second point to the first) yields the complement of the forward azimuth ((Az + 180º) mod 360º). For great circles, the back azimuth is generally not the complement, and the difference depends on the distance between the two points.
In addition to forward and back azimuths, Mapping Toolbox functions can compute locations of points a given distance and azimuth from a reference point, and can calculate tracks to connect waypoints, along either great circles or rhumb lines on a sphere or ellipsoid.
For more an example that uses azimuths, see Determine Destination Given Starting Point, Initial Azimuth, and Distance