Could someone explain this Critical angle >sin^-1 (n1/n0) in words?

This Link gives a nice explanation. Let me know if you have any questions.

The critical angle (where transition from refraction to total internal reflection occurs) is the angle whose sine equals the ratio of indexes of refraction.

The critical angle is where light is refracted at an angle such that it cannot fully pass into the less dense medium, but traverses parallel to the barrier between the two media.

This is the smallest angle to the surface normal at which total internal reflection occurs; the word definition would probably depend on the point of your powerpoint.