What is the difference between glue and glueless vinyl flooring?

The difference between glue down and glue-less vinyl flooring is in the thickness of the planks and in the installation. The glue down vinyl flooring is 2mm thick and requires an adhesive to bond it to the subfloor. The glue-less planks are 4-5 mm’s thick, have a 4 sided locking system and they click together for easy installation.