An assembly is

• in politics, any body meeting together to discuss matters, a parliament or a legislative assembly such as the French revolutionary Legislative Assembly, or a body more designed to mediate between otherwise independent bodies, such as the United Nations General Assembly.
• in mechanics, architecture and electronics, the action of putting together the separate parts of what is intended to be assembled. Modules, components or elements or combinations of such may be the objects of the assembly. "Assembly" may also refer to the whole that results from such action.
• sometimes, in schools, a body collecting the students together for prayer, song, bible readings and a moral message.
• in Microsoft .NET, a building block of an application, similar to a DLL (a Microsoft shared library), but in addition to containing executable code, an assembly also contains information found in a DLL's type library. The type library information in an assembly, called a manifest, describes public functions, data, classes and version info. See .NET Framework Developer's Guide, Assemblies

You might also mean:

• Assembly language
• Assembly demo party