A subgenre of emotive hardcore and indie rock that formed in the 90's. Screamo isn't mainstream and you will not hear any screamo bands played on the TV or radio.
Some real screamo bands are Orchid, Pg.99, Circle Takes The Sqaure, City of a Caterpillar, Piano Come The Teeth,
Saetia,
Anomie, Portraits of Past, I Would Set Myself On Fire For You,
Indian Summer and The Saddest Landscape.
Screamo is often a term used for bands like Bring Me The Horizon, Asking Alexandria, Pierce The Veil, Escape The Fate, Falling In Reverse, Sleeping With Sirens or any other band that has used the technique in their songs. Anybody who says these bands are screamo is wrong, they are post-hardcore or metalcore.
They're part of the metal mainstream.