ATEX stands for ATmosphere EXplosible. ATEX pertains to explosion-proof electrical and mechanical equipment, components and also protective systems. It lies under the European Directive 2014/34/EC and applies to the manufacturing of products which may be used in potentially explosive atmospheres.
It is worth mentioning that it is at the manufacturers responsibility to ensure that any products that fall within this category are compliant with the aforementioned Directive.