Something that's ignored is overlooked, neglected, or disregarded, perhaps deliberately. An ignored deadline for turning in a homework assignment will likely result in an unsatisfactory grade.
A party guest who is ignored may have hurt feelings, and not stick around for long. But those ignored spiders in the corners of your ceiling will likely stay indefinitely, happily undisturbed up there. The adjective ignored stems from the Latin root ignorare, "take no notice of." Some things, like taunts from bullies or spoilers that give away the ending of an upcoming movie, are best ignored.