Definition: Describes a site on a sequence, i.e. the position of a single nucleotide or amino acid. Usage: A sequence site is always defined based on the reference sequence of the owning entity. For DNARegion and RNARegion it is relative to the region itself not the genome or full RNA molecule.
Source:http://www.biopax.org/release/biopax-level3.owl#SequenceSite