A modular synthesizer has a case or frame into which arbitrary modules can be plugged; modules are usually connected together using patch cords and a system may include modules from different sources, as long as it fits the form factors of the case and uses the same electrical specifications.
A semi-modular synthesizer on the other hand is a collection of modules from a single manufacturer that makes a cohesive product. Modules may not be swapped out and often a typical configuration has been pre-wired. However, the manufacturer provides mechanisms to allow the user to connect modules in different orders.
Bon c'est juste une histoire de sémantique, au final ce sont des outils pour faire de la musique !The VCS 3 (or VCS3; an initialism for Voltage Controlled Studio with 3 oscillators) is a portable analog synthesiser with a flexible semi-modular voice architecture, by Electronic Music Studios (London) Limited (EMS) in 1969.[# 1]