Industry is the 'building resource' of Dungeon of the Endless; it allows you to build things such as major and minor modules. Without any modules to increase industry, it is set at +3 every door opened. The amount of industry it costs to build major modules increases with each subsequent module built, whereas at the moment minor modules do not do this.
As mentioned previously industry gets increased by +3 every door regardless of modules. However, you can build an Industry Generator that will increase the output of industry per door. Industry can also be gained by coming across random generators that spawn in random rooms that usually grant around 6-10 industry.