Print-on-demand is simply a method of producing a printed book. Some commercial publishers will do that, rather than risk large offset runs which may have to be brought back and pulped when they don't sell.
Most agents, in thrall to the old paradigm, consider POD books as being suspect, if not not downright sacrilegious. Don't forget, to them any form of self-publishing represents Armageddon, and they are therefore not in favor of it.
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