Subdivision of
emo and
hardcore, generally having more similarities to hardcore in terms of instrumentals, but lyrics are closer to emo. Screamed or spoken-word vocals, laden over soft, proggy riffs or crashing metal madness, more the latter. Mostly dead by now, as the genre was already heavily explored in the 90's by bands such as Hot Cross, Saetia and Orchid.
Most modern (post-2000, really) bands referred to as screamo are either
emocore, such as Alexisonfire and Thursday, or
mall punks wearing eyeliner and trying to be scary, such as The Used and My Chemical Romance. Derision should not be layed against such mall punk bands, however, as they still have enough balls to wreck their vocal chords while singing about how they're just kids and thier lives are nightmares.
"Man, this Level-Plane screamo stuff is way too hardcore for my ears. But hot damn, those are some cool riffs." CORRECT
"The Used is a great screamo band." INCORRECT