what is a sizzle reel?

Come across a new expression - and figuring out what it is...
A sizzle reel is a leak, a trailer, a documentary of a project. a deliberate programme made during a bigger production. the opposite end to the 'extras' that would be on the DVD. it is a promotional hype of a larger project after production has been granted.
heres one for Walking dead - that is due to launch in late October.
(that is almost worth a study in itself - with the history of the walking dead comics)


But a Sizzle reel, includes shots from the film - key shots but not spoilers. interviews with cast and crew, short vox pop though not in depth. it is almost a twitter of the film. statements of less than 180 characters.

they cover conferences too; lay a 'Rock' track down - a few timelapse clips of 'people' soound bite interview of delegates just as they have got off stage - bingo cymbal finish - this one chimes all the gongs - they are usually about 4.30mins and finish with a great big pat on the back for themselves