Soft System (glossary)
A system that is characterized by extremely complex, problematical, and often mysterious phenomena, for which concrete goals cannot be established and which require learning in order to make improvement. Such systems are not limited to the social and political arenas; they also exist within and amongst enterprises where complex, often ill-defined patterns of behavior are observed that are limiting the enterprise's ability to improve. (Checkland 1999)
Checkland, P. B. 1999. Systems Thinking, Systems Practice. Chichester, UK: John Wiley & Sons Ltd.