RSS is an exchange format for web-content.
Its main purpose is to pass messages and other information in a standardized format over the internet.
Differently from a normal website, the information in a RSS file is reduced to the actual content.
It is also marked with special tags, so that machines can interprete the content.
In contrast to ordinary website, RSS-files can be read and processed from other software.
The most common of these are the RSS-readers.
They can watch every update of a website and then display the changes on demand.
The use of a RSS-reader can save you time, because several news- or weblog-pages can be subscribed
and the associated website visited only if desired.
Thus you can have an overview of your sites of interest without the need to visit each one after the other
with a browser.
RSS on Wikipedia