The modular synthesizer is a type of synthesizer consisting of separate specialized modules. The modules are not hardwired together but are connected with patch cords, to create a patch. There are both audio and control signals, which are interchangeable.
Read more about Modular Synthesizer: Types of Modules, Historic Manufacturers of Modular Synthesizer Hardware, Modern Manufacturers of Modular Hardware Synthesizers (alphabetical), Modular Software Synthesizers (alphabetical), Semi-modular Synthesizers, Hybrid Modular Synthesizers