Both are the different names for essentially the same thing. Yahoo! Connected TV is an internet connected TV or set-top-box that gives access to "applications" on your TV. Yahoo! Connected TV is an open platform to develop your own app for distribution across all manufacturers that support Yahoo! Connected TV (Sony, Samsung, LG, VIZIO, D-Link, Vestel, Hisense, Toshiba).
Samsung, and others, are pushing the "new" term "Smart TV" to refer to internet / computation enhanced TV products in general. Back formed, or formed to echo "smart phones" (with all the implied rigor of definition and marketing hype I am sure.) See: http://www.splatinteractive.tv/2011/01/giv...-name-smart-tv/