Originally, RSS (version 0.9) meant Rich Site Summary and was RDF-based. Then UserLand, dubbing it Really Simple Syndication, created version 0.91, which was a generic XML format. As 0.92 through 0.94 were being developed, an open group created RSS 1.0, which returned RSS back to its RDF roots, and dubbed it RDF Site Summary.
Now RSS 2.0 is being designed to mix the simplicity of 0.93 with the extensibility of 1.0. Though, there have been many arguments about the leveraging of simplicity and extensibility of RSS 2.0 (is it too complex, does it have enough features, etc.); so Aaron Swartz, ridiculing the heated debates, made a specification for an extremely easy version 3.0, which is sent as traditional lines/fields.
Now that the history lesson is out of the way, it must be said that none of these initialisms really embody what RSS is. RSS is often used for site summaries; but sites that do this generally have "topic summaries" with many feeds per site. And RSS is also used for syndication. But these are not the only uses. One overlooked possibility is software updates. People hate subscribing to notification (and other mailing) lists, and only a fraction of usenet messages are relevant, but RSS is the ideal way for users to get the information they want, all collected by a program for convenient reading.
It's not really better, though there are two main advantages. First, RSS 3.0 is smaller, which makes downloading it quicker and is less of a strain on the server. Second, it's easier to write. RSS 3.0 has maybe a half dozen mandatory rules; whereas XML is, frankly speaking, an overkill for simple news and site summaries.