What makes a drink dirty?

In the context of mixed drinks, the term "dirty" refers to the addition of olive brine or olive juice.

For instance, a "dirty martini" is a martini prepared with a small amount of olive brine or olive juice, while a "dirty Shirley Temple" is a non-alcoholic mocktail made with ginger ale, grenadine, and a splash of olive brine.

The addition of olive brine or olive juice can add a salty and savoury flavour to a drink, as well as a slightly murky or cloudy appearance, hence the term "dirty".