RSS compatible site design

In some of the new websites I am designing, the clients are asking for it to be "RSS Compatible".
I understand that there is a certain 'schema' things must adhere to, but I'm a little bit confused as to how this is typically achieved. Does ALL of my content have to exist only in XML for me to have an RSS compatible site, or what? I've never done anything with RSS and it's very confusing to break into because it seems to assume a lot of things that make little sense.

Does anyone have the ability to shed some light on this?
veruthandaiAsked:
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