Total internal reflection is an optical phenomenon that happens when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.
All of the light is reflected.
Question asked: Is this like a mirror?
Answer: No. A mirror only reflects about 90%, the other 10% gets absorbed by the mirror's silver plating or is reflected away from the main image. Since silver oxidizes, a silver mirror can wear out. However, with TIR to reflect light, it will be everlasting.
1) Used in high quality optical devices like periscopes, expensive binoculars or cameras.
2) It is a fundamental part of fiber optic transmission, one of the fastest ways of transmitting information. This is due to the fact that ALL light is reflected using TIR.