In bartender's parlance, a "dash of bitters" is the equivalent to a few drops. In almost all cases, the bitters in question is made by Angostura Limited.
Bitters is a common ingredient in a number of mixed drink cocktails, such as the Bloody Mary, champagne cocktail, Manhattan, Mojito and Rob Roy. Angostura bitters contains a combination of herbs, water and 44.7 percent alcohol. In addition to the original recipe for bitters, Angostura also makes Orange Bitters, which is made in a similar manner to regular Angostura bitters and is then infused with orange zest. In addition to mixed drinks, bitters is also used in main courses like shellfish and fish, as well as in soups and sauces.