M&M's (styled as m&m's, pronounced emenems) are "colorful button-shaped chocolates" produced by Mars, Incorporated. The candy shell, each of which has the letter "m" printed in lower case on one side, surrounds a filling which varies depending upon the variety of M&M's. The original candy had a milk chocolate filling which, upon introducing other variations, was branded as the "plain" variety. "Peanut" M&M's, which feature a peanut coated in milk chocolate, and finally a candy shell, were the first variation to be introduced, and they remain a regular variety. Numerous other variations have been introduced, some of which are regular widespread varieties (such as "peanut butter", "almond", "pretzel", "crispy", and "dark chocolate") while others are limited in duration or geographic availability.