Widely accepted qualitative statements that, as judged from examples, add structure to ill-defined situations (Rechtin 1991)
Rechtin, Eberhardt. 1991. Systems Architecting: Creating and Building Complex Systems. Englewood Cliffs, NJ: CRC Press.
Rechtin has at least five defintions of this term. However, they are not sufficiently different to warrant listing them all. This one is typical.