OSGi stands for Open Services Gateway initiative. Governed by the OSGi Alliance, OSGi defines a dynamic module system for Java. It specifies a way to build applications from reusable, collaborative components and a platform for these components to dynamically interact with each other.
The OSGi Alliance is made up of companies, government organizations, education centers who all support the adoption of OSGi technology. For a detailed overview of OSGi have a look at the OSGi technology overview.