Measure
Part
A part is a proportion, not a fixed amount: "2 parts gin, 1 part vermouth" means twice as much gin as vermouth, whatever size you use.
In practice
Pick one measure, such as a 1 oz jigger, and use it for every part. Parts make a recipe easy to scale up for a pitcher. When a recipe gives only parts, Drinky-Drink works out amounts for one drink.
Drinks to try it with
Part, in short
What does part mean?
A part is a proportion, not a fixed amount: "2 parts gin, 1 part vermouth" means twice as much gin as vermouth, whatever size you use.