It’s blanching marinated chicken in oil or water prior to stir-frying, thus tenderizes the chicken.
Oil-velveted chicken is firm, while water-velveted is soft and bouncy. I like the water-velveted because of the texture, and water is easier to dispose than oil when done.
When velveting in oil, you want to heat the oil to 275, and cook until they are 90% done, while stirring. Drain immediately and let cool.
When velveting in water, bring the water to a simmer, never a boil. Then allow them to cook until they are 90% and drain them.
Once velveted, the chicken should be stir-fried immediately.