This is a unit dimensionality used in quantities. Quantities with a dimensionless unit are just counts. They are not an amount of some unit like feet, meters,or kilograms. They are just a count.
Various dimensionless units are dozen, percent, gross. Dimensionless quantities can multiply or divide any other unit. For example if you have a quantity such as 5 square meters you can multiply it by a dozen to get 60 square meters, or divide it by 5 to get 1 square meter.