The doomed are people marked by very bad luck, particularly death. When you learn about a tragedy, like a tsunami that kills many people, it makes you feel terrible for the doomed.
Doomed is a plural noun for referring to a group of unfortunate people, and it's also an adjective describing someone who's destined to die. A runaway dog that kills the animal control officer's pet chickens is doomed, and many characters in Shakespeare's tragic plays are doomed. You can also follow doomed with "to" to mean "destined" or "fated." Your uncle might be doomed to continue working as a school bus driver for the rest of his career.