When discussing food sources of protein, nutritionists often speak in terms of "complete" and "incomplete" proteins. Foods that provide complete protein are those that include all of the essential amino acid, while foods that provide some or none of the essential amino acids are said to be incomplete.
Eggs, dairy foods, meat, fish and poultry are typically considered to be complete proteins. Vegetarians, and especially vegans, often do not have a source of complete protein in their diets, but can easily obtain all of the essential amino acids by eating a variety of beans, grains, nuts, seeds, and vegetables.