To poach means to cook foods in a liquid just below the boiling point, or at a simmer. Protein foods tend to become tough when boiled.
Whether foods are cooked in a lot of liquid or very little, we shall refer to the method of cooking protein in liquid as poaching.
The liquid may be seasoned court bouillon, wine court bouillon, milk court bouillon, chicken or beef stock, white or red wine, mushroom broth, milk, cream, tomato juice, or any combination of these, as well as others, such as vermouth, beer, or even water.