A number of photo inkjet printers use two different primary black inks - Photo Black or Matte Black. Each is optimized for a certain type of inkjet media.
Use Photo Black for glossy photo paper and satin / luster photo papers. Some fine art media like baryta photo paper and platine type photo paper also require the use of Photo Black inks. You will use Matte Black inks for cotton fine art and matte inkjet media. Matte papers are usually smooth and have a flat non-reflective surface.
Older Epson printers like the Epson R2400 and Epson R2880 require that you physically change the ink tank when you want to switch media types.
Newer Epson printers, and all Canon printers (with multiple black inks) have all of the ink tanks on the printer at one time. The machine will either automatically switch when you change paper settings, or it will do a short "ink swap" then proceed with printing.