The glancing angle is defined as the angle between the ray of the incident on the plane surface and the surface. An example of a glancing angle is a beam of electrons incident on the crystal.
Also, there is a glancing angle of reflection and the glance of incidence.
The glancing angle of reflection is the angle between a surface and a beam of particles. It is the component of the angle of reflection.
The glancing angle of incidence is the angle between an incident beam and the surface. It is the component of the angle of incidence.