Bleed Margin

I am going to be doing a digital art project with some artists and would like some explanation on the bleed margin.

I looked up the definition online and I think I know what it's referring to. In regards to doing something in photoshop for example, lets say a page with a gradient overlay on it, that fills an 8.5 x 11 inch document, or a standard pag size. There is always a white border when I print it out on photo paper.

With that said I'm guessing the bleed margin is that space that is removed if I have a professional printer, print the pages, is that correct?

If not, can someone explain the advantages and disadvantages of the Bleed Margin?

Thank you,

Invision

yea im pretty sure thats what it is, i worked wit some before but i never really new, i kinda jus ignored them..lol. But thats wat i would assume a bleed margin is.