What are polyps? Anyone ever had one?

Today, my Dr said he thought he saw a polyp in a sonogram I had before having an IUI in late July. He said I would have to come in later for another sonogram to be sure because sometimes they 'come & go'. He also said that if I did have a polyp he would have to perform a D&C to get rid of it. He didn't elaborate anymore. How serious is this? How is a D&C performed? Will I ever be able to get pregnant afterword - will having a D&C improve my chances of becoming pregnant? Any information will be appreciated!