An Acronym with a variety of expansions, all referring to the same thing:
- Rich Site Summary (RSS 0.91)
- RDF Site Summary (RSS 0.90, RSS 1.0)
- Really Simple Syndication (RSS 2.0)
- no expansion at all (RSS 0.92-0.94)
There are 9 different incompatible versions, but the point is always the same: they're XML vocabularies (and some of them are RDF in XML form) for expressing NewsFeeds.