What is the difference between an atomizer and cartomizer?

The main difference is in the construction of the electronic cigarette. If you have a separate atomizer and cartridge then you will be using a three piece electronic cigarette. Most companies have switched over to using a two piece electronic cigarette which combines the cartridge and atomizer - hence the name “cartomizer.” The cartomizer is a cheaper and better functioning unit than when the atomizer and cartridge are separate.