SARG stands for "Search ARGument" and "SARGable" has come to mean that the search arguments in a WHERE clause, ORDER BY, and/or ON clause are capable of doing an INDEX SEEK if the appropriate index is available and used.
Search arguments that modify a column will only allow for either a table scan (includes Clustered Index Scan) or a non-Clustered Index Scan.
--Jeff Moden
Change is inevitable... Change for the better is not.