On the Rocks
The expression, “on the rocks” refers to serving an alcoholic beverage over ice. The expression literally refers to the ice cubes as rocks, so it becomes an idiom. It is really the guests’ decision about whether or not they would like their drink served over ice, although some drinks are normally served with ice. Having ice in an alcoholic drink chills the contents but also dilutes the alcohol content of the drink.
Straight shots are often served on the rocks in order to chill the liquor and tone down the taste of the alcohol itself. Bartenders can use the “on the rocks” expression to inquire whether or not guests want ice served in their soft drinks but it isn’t as common.
