This article by @L0la L33tz is interesting.
According to L0laL33tz The SEC (U.S. Securities and Exchange Commission) expands their definition of what an exchange is to be inclusive of:
"systems that bring together buyers and sellers of securities that offer the use of non-firm trading interest and provide another type of non-discretionary method (i.e., communication protocols). The proposed amendments would require these systems to register as national securities exchanges or as broker-dealers and comply with Regulation [Alternative Trading Systems] ATS."
@L0la L33tz, please site where this quote is taken from.