A highball glass is a larger tumbler which can hold roughly 8-12 fluid ounces and often is a substitute for the more rare collins glass. Typically, the highball glass is used for cocktails that have a higher degree of non-alcohols such as orange juices, pineapple juices and other fruit flavorings.
Higher than an old fashioned glass and fatter than a collins glass, the highball is a very common glass used in many great recipes.