SAS is the acronym for Self Aware Substructure. Coined by cosmologist Max Tegmark, it refers to the
idea that self aware entities must necessarily exist as
sub-systems within a larger systematic structure. Presumably, there are other possible complex, systematic structures than our own universe, that are capable of producing types of self aware substructures
aka intelligent beings.
"Given a mathematical structure, we
will say that it has
physical
existence if any self-aware substructure (SAS)
within it subjectively perceives
itself as living in a physically real
world." - Max Tegmark, arXiv:0905.1283