A footprint defines the basic "stuff" that goes on a PCB so that a device may be soldered to the PCB.
This page has been checked to see that confusion in my brain (before 9 November, 2011) about the roles of pin names and pin and pad numbers hasn't led to errors here. I have a page with more on this if you are really curious.
In simple terms, there is a 1:1 relationship between the components in the schematic and the footprints on the PCB. However, life isn't always simple, and sometimes a single actual physical package (or device) may contain multiple gates, in which case a number of components may all be catered for by a single footprint. (The site has an essay on multiple gates for you.)
One of the interesting and powerful features of KiCad is the flexible and ad hoc matching of components and footprints which is made possible by the approach used internally by KiCad. A given component may map to one footprint in one project, but to a different footprint in another project. You can even have multiple associations within a single project. The device (e.g. a capacitor) with "C1" in it's "reference" field might use the same component as "C2". Of course they will both map to separate footprints on the PDB design… but it isn't necessarily true that both of them are of the same type. You might want a little capacitor with radial leads for C1, but a big capacitor with axial leads for C2. They each need a footprint, and each needs a different sort of footprint. KiCad handles all of this easily.
(Building the internal table of mappings is the job of CVpcb)
The terms "footprint" and "module" both appear in KiCad. I have yet to grasp the distinction between them, if they are not mere synonyms.
A detail…
Beware: The wiki you are reading was created with the excellent, free, service from http://Wikidot.com. They use the term "module" too! I have tried to bury WikiDot's use of the term "module". If it still appears on the site in a place which might confuse a beginner, please write, tell me where?)
