This paper introduces the SAREF reference ontology pattern SAREF4SYST, which defines systems, connections between systems, and connection points to which systems can be connected. These basic concepts can be used generically to define the topology of entities of interest and can be specialised for multiple domains. SAREF4SYST has already been reused or aligned to in different domains related to cyberphysical systems, including electrical power systems, smart buildings and smart lifts, communication networks, and multiphysics simulations.