The Old Fashioned is a cocktail.

Recipe:

• 2 oz. rye whiskey or Bourbon
• splash of simple syrup or 1 cube sugar and just enough water to dissolve it
• 2 dashes bitters
• 1/2 orange slice
• Old Fashioned glass

Muddle orange, sugar (or syrup) and bitters together

Fill glass with ice and add whiskey

Garnish with maraschino

Under no circumstances is soda to contaminate this cocktail if it is to be considered an Old Fashioned.

An 1895 recipe specifies the following: Dissolve a small lump of sugar with a little water in a whiskey-glass; add two dashes Angostura bitters, a small piece ice, a piece lemon-peel, one jigger whiskey. Mix with small bar-spoon and serve, leaving spoon in glass.

Renewing an Old Fashion discusses the history of this cocktail.

See also the Wikipedia Cocktail Guide.