Spoilers are experts from the real boom or story, that you may not know of yet. This is to tell you that if you have not read the book or story but plan to, but don't want to ruin it, to not read that fanfiction. The parts of the novel you may not know yet are written in the text. See fanfiction for more information on those.
"Hey Sarah, this now HP fic has spoilers in it for the new book. Should I read it?"
"Not if you want the boom to be a surprise, Judy".
An aerodynamic device used on tractor-trailer trucks. A spoiler is located on the roof of the tractor which deflects air from buffeting the trailer. Truck roof spoilers increase the top speed of the truck, save diesel fuel, and protect the refrigerator coils of refrigerated trailers from rocks that blow off of dump trucks.
The top speed of this Kenworth is 117 miles per hour, the same truck without the Spoiler only goes 113 MPH. By the end of the day I'm 64 miles ahead, because I have a Spoiler.