Light being entirely reflected back into the first medium is a condition called:

1. The condition has a standard name. 2. Beyond the critical angle, no light crosses into the second medium. 3. All of the light is reflected back into medium 1. 4. That condition is called total internal reflection. _Source: OpenStax College Physics for AP Courses 2e (CC BY 4.0), Ch 25 'Geometric Optics', sections 25.1-25.7_