According to the current state of practice, highly complex systems are no longer specified by comprehensive, monolithic models. Instead, relevant behaviours are represented separately as parametrised scenarios, and the overall system behaviour is derived from the resulting scenario library. This library concept has originally been advocated for the purpose of creating test references for autonomous road vehicles. Currently, scenario libraries are the preferred approach to specify the expected behaviour of any type of highly complex systems, both as an input to the design phase and as a collection of reference models for testing campaigns. In this paper, we introduce the novel scenario specification language SCSL and explain its syntax and semantics. In contrast to existing scenario modelling alternatives that are tightly bound to a specific application domain, the SCSL is domain-independent, but domain-specific support can be added in the form of re-usable specification libraries.