In Suzanne Cook's blog there is such a description:
LoadFrom Context: In general, if the user provided Fusion a path which was used to find the assembly (and the assembly at that path wouldn't have been found in the Load context), then it's in the LoadFrom context. There are various methods to load by path: LoadFrom(), CreateInstanceFrom(), ExecuteAssembly(), loading an assembly through interop using a codebase, etc.
And also I found an MSDN article about it but I am not really sure whether the Fusion Suzanne talks about is same as here: http://msdn.microsoft.com/en-us/library/e74a18c4(v=vs.71).aspx but it seems a Log viewer so what I understood what Suzanne says is
Fusion is a probing mechanism which takes path, etc and it probes assemblies in Application Base,
codeBase
, GAC, etc. to load them into the context.
Some one can clarify this please?