While the meanings of the terms are not set in stone, "framework" is usually used to mean a support sub-system that is rather invasive and defines how you write applications using that framework. GWT is one example, Struts is another.
The term "library" is usualy take to mean support code that aids you in writing applications, but does not impose a methodolgy of its own. Prototype, Scriptaculous and jQuery are some client-side examples.
Again, these terms are not precisely defined anywhere, so others may have their own definitions.