This is sometimes abbreviated to TIR. Total means that all the light is reflected. None of it escapes out by refraction. The first example I will show you is with white light and a glass block, showing how we can adjust the amount of light reflected. Later we will look at another example with red light.
White light demo
Did you see as the angle of incidence increased, more of the light was reflected and none escaped? This property of total internal reflection is used in optical fibres. Light travels down the fibre in a series of reflections. This can allow the passage of light down a whole bundle of fibres.
Now we will look at a series of total internal reflections with red light.
Did you see how the red light bounced between the outside surfaces of the glass blocks? The same thing happens inside an optical fibre. The angle of incidence (in the glass block) has to be more than 42 degrees for total internal reflection to work.