A "set" is also known as a "lot". This term refers to how many units of something are printing at the same time. Let's say you are looking to print business cards for 10 people in your office. If all ten (10) orders of business cards being printed have the same parameters or specifications (ie: same quantity, same paper stock, etc), but each only has different ARTWORK, then it would be considered 10 sets or lots. If the product you are ordering has this option enabled, you will see a "Total Sets". Simply select from the drop down menu the number of units you need.