Define Glancing angle.

Hint: Here in order to answer the question we will learn about the concepts of glancing angle, relation between glancing angle and angle of incidence and how it is useful to us.

Complete step by step solution:
The glancing angle is the angle formed by the incident ray on a plane surface and the surface itself. A ray of electrons striking the crystal is an example of a glancing angle.
A glancing angle of reflection and a glance of incidence are also present.
The angle formed by a surface and a beam of particles is known as the glancing angle of reflection. It's the angle of reflection's part.
The angle formed by an incident beam and the surface is known as the glancing angle of incidence. It's the angle of incidence's part.
Consider the incident of a ray of light, AO, on a plane mirror, XY (Figure) at O. It's mirrored all the way down OB. The glancing angle with the mirror is the angle AOX made by AO with XY.


Note:
The distinction between angle of incidence and glancing angle must be understood. The angle of incidence is the angle established between the normal and the incident ray at the point of incidence. The angle between the beam and the surface, rather than the angle between the beam and the surface usually, is also more useful, i.e. 90° minus the angle of incidence, known as glancing angle.