Whey protein is one of the two proteins found in milk (the other being casein). Whey is a complete protein, meaning it contains all amino acids human need nutritionally. It is the most absorbable protein for supplementation.
Whey protein is a product of cheese manufacturing, so in many situations it is processed heavily even before it has made to whey. There are risks of contamination as well as adulteration (spiking with foreign compounds like drugs). Since whey comes from milk production, concerns about the farming process arise quickly.
We recommend minimally processed whey proteins. We use brands whose whey comes from New Zealand cows as they are grass fed and hormone and antibiotic free.