Mayo is a thick, creamy dressing mostly used as a condiment. Mayo is a stable emulsion of oil, egg yolk, and either vinegar or lemon juice, with many options for embellishment with other herbs and spices.
Proteins and lecithin in the egg yolk serve as emulsifiers in both mayonnaise and hollandaise sauce. Commercial egg-free alternatives are available for vegans and others who want to avoid animal products and cholesterol, or who are allergic to eggs. In the United States, mayonnaise sales are about $1.3 billion per year.
You can use Mayo in Burger Recipe. See use of Mayo here