Starmaker: Huh, what's that all about?
CharlesGrey: The license agreement only allows the engine to be used for games that are designed for entertainment. In other words, you aren't (legally) free to use it for arbitrary purposes; in particular, you can't use it to do a physics simulation, for example.
An example of what would likely qualify as a "Serious Game" is Depression Quest. Depression Quest is meant to teach its players about depression, and according to the intro, is not designed to be fun. (Of course, one could probably think of other, less depressing games that would qualify as "Serious Games" under the license agreement's definition.)
This sort of thing is why I would rather use an open source engine or write my own; that way I don't need to worry about this sort of restriction. (The CryEngine license agreement violates at least clause 6 of the Open Source Definition.)