A meme from the Lostpedia forums. It started when someone made a very badly worded post asking if anyone had seen an "invisable dinasaur head" on a recent episode of Lost.
"Hed" was not actually said in the original post, but it ended up being morphed into that by other posters.
After a few pages, the thread became about taking quotes from normal posts on the Lostpedia forums and putting them over screencaps from Lost to make it appear like the characters are saying those things. The thread currently has 17,368 replies and counting.
The meme has even been recognized by the writers of the show after it was entered several times into a contest to decide the name of the finale episode of Lost. Damon and Carlton, the writers, joked about the name and called it the "worst finale codename".
Have you heard about the invisibul dinasaur hed on Lost?