"Sets if the product can be sold in quantity increments. If enabled, enter the quantity of products that must be purchased in an incremental step."
(ex. 2,4,6,8, etc. or 3,6,9,12, etc.)
There are other ways of addressing this issue, like using Tiered discounts to offer price breaks for shoppers purchasing higher quantities of your products, and bundled products, which will allow you to offer discounts to shoppers that purchase particular items together.