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Graceland is the name of Elvis Presley's estate in Memphis. (More here) But what Simon does with his album is borrow some really beautiful instrumentation, chanting and howling from the traditional music in Africa. Yes, howling. It's great to listen, btw.
If S&G were singing sweet ballad like songs with enchanting lyrics, then Graceland is in part African, in part Jazz, in part Rock n Roll and in part Rock music.
While Graceland found its way into Rolling Stone's best 500 albums ever list, it was also taken to task by some reviewers like this one.
But I have now listened to it more than a few times and I really do like it. I find it a liberating experience to listen to music which is from the 'other'.
Some of my other posts about rock music are here.