A campaign is a large, often epic, story that spans numerous single adventures and ties them together into a cohesive and meaningful whole. A campaign is usually composed of multiple modules (or chapters), with each module automatically starting as the preceding one ends. Usually, the order in which the modules are played is preset, but there may be less linear play within a module.
There are three official campaigns (developed by BioWare) that were included with Neverwinter Nights and its two expansion packs.