Can we Define "Spoiler" Please?

[TruCelt]

In this week's "House" thread there is a poster complaining about being "Spoiled" because somebody mentions what was shown in the preview for next week. The publicly shown on television, planned and approved by the director, producers, etc of the show, preview.

Now, I acknowledge that there is a group of people for whom this stuff matters, for whom it truly ruins the experience, and that I am at the full opposite end of the spectrum. (I'd much rather know what is going to happen so that I can enjoy the artistry of the exposition.)

As the level of bitterness that results is pretty extreme, and as there is certainly a field of grey within which to make claims of spoiler-ing (spoilage?); I think the board might benefit from an accepted definition.

I am probably the wrong person to try and define what that should be, but I think it should include the statement that trailers, previews and scenes widely shown in commercials or other promotional materials on the public airwaves are free game.