A musical genre that often goes hand in hand with screamo, metalcore and hardcore punk. A main feature of the genre is the contrast of melodic and/or emotional singing with screaming, and sometimes other vocal styles, like whispering, yelling, etc. Fast-paced hardcore/thrash metal guitar riffs and high-pitched, heartfelt melodies are another example of the contrast commonly used within this genre. Kind of like a mixture of emo and thrash.
Some good examples of post-hardcore are:
From Autumn to Ashes
Thursday
My Chemical Romance (on their first album)
Glassjaw
Alesana
Haste the Day
Underoath
Atreyu