What is casein?
Casein is a type of protein.
Like whey protein, casein is also a protein of high biological value, although inferior to whey, and as such contains all the essential amino acids.
Casein, unlike whey, is a slow-absorbing protein and is therefore normally used before bed, as it will provide amino acids to the body for several hours, which is ideal while we are sleeping.
It can also be used in other meals to increase the protein content, as in the case of whey.
Find good examples of casein supplements here.