A Highball is a cocktail made with a spirit and a non-alcoholic mixer. The mixer is almost always a majority of the volume of the drink, so these tend to be lighter, more refreshing cocktails than those in the other drink families. A classic highball is a whiskey highball, made with 2 oz whiskey and 6 oz of soda water. Highballs are staples in homes across the country, from Jack and Coke to gin and tonic, because they tend to be forgiving of un-measured pours.
A highball doesn’t have to be mixed with soda. An Irish Coffee is mixed with coffee. A Bloody Mary is mixed with tomato juice. Other highballs are mixed with juice.
Credit for the six cocktail families goes to Cocktail Codex. I highly recommend it for an in-depth exploration of drink variations in each category