A member of a technical writing discussion group asked if the term should be Manual or Guide for user documentation.
In my experience, both Guide and Manual have been used to mean the same thing. Often, a shortened version is called a “guide,” while the larger, longer manual is called a “manual.”
However, to me, the more important distinction is whether the documentation is a reference manual (or guide) or a how-to manual (guide).
The difference is that a reference manual tells you what features/functions are available, but not necessarily how to engage those features/functions. A how-to manual tells you how to engage at least some of the features/functions available.
Booker's Blog 