A non–featured artist is someone who performs on the recording but is not the main credited act. For example, remixers, session players or backing vocalists. They might earn certain “neighbouring rights” royalties on the recording side, but they are not normally considered writers unless they contributed to the composition, and in the case of remixers, if the original composers agree to give them a share (which is rare). This operates both ways of course, since a remixer of your composition is not normally entitled to a share of royalties.