This means that the ham is sliced on demand, or if you're v lucky, hand-carved, making it a lot more expensive than a whole piece, or a pre-sliced pack.
As for leaving jamón ibérico tal cual, I would recommend this, followed by an explanation: (Premium) (Spanish) Ibérico Cured Ham, or something along those lines.

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Note added at 8 mins (2007-05-31 14:01:27 GMT)
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http://www.brindisa.com/retail_carving.asp
Brindisa are pretty hot on their ham (they import stuff made from our pigs, je je!), and this page has good comments and a good pic at bottom.

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Note added at 1126 days (2010-07-01 09:18:05 GMT) Post-grading
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http://www.brindisashops.com/ham/whole_spanish_hams/

New link, since the old one no longer works. There's a paragraph on what exactly Jamón Ibérico is.

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Note added at 1126 days (2010-07-01 09:24:46 GMT) Post-grading
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"La Denominación de Origen jamón de Huelva ampara los jamones y paletas de cerdos ibéricos alimentados de forma natural y en régimen extensivo." http://jamoniberico.com/

Steven is right to say that Jamón Ibérico is not a DO in itself. However, I am a staunch advocate of leaving the wording in the original, with explanation where appropriate. Among other reasons, this is because by extension, if you translated, one standard starter in restaurants would be a "Iberian (charcuterie) platter/platter of Iberians" (for "Surtido de Ibéricos") which, qute frankly, I don't think would do!!