2) A flash program with a massive shift in volume. It will usually start up low so you have to put your speakers up, then will emit a loud 'scream' literally out of nowhere.
1) I had to put a pillow on her head to keep her from waking up her parents, she was such a screamer.
2) That flash program which plays the song really low backwards is a screamer.
A scary practical joke where the victim watches a video.
They watch THE VIDEO.
So, they are forced to watch the whole video, when suddenly, a loud scream with a scary image pops up on the victim. The victim is now scared.