ssebmly is Unit deployment like EXE or DLL.

An Assembly consist of one or more files(dlls ,exe's ,html files etc), and represent a group of resources, type definations and implementaions of those types.An assembly may also contain refernce to other assembly.These resources,types and refences are described in a block of data call a manifest.The manifest is part of the assembly,thus making the assembly self-describing.

--Ajay joshi