I only know one meaning. It is capitalized, "Shrek," because it is a proper noun. It the name of a fictional, green, animated character in a series of movies. A Google Images search will show you what Shrek looks like. The German word for "fright" is "der Schreck" and that influenced Shrek's name. He is actually a very nice, kind-hearted character, but he looks frightening.

Shrek is a popular animated character in the Shrek films that tells the story of a giant green ogre. Perhaps you mean shriek? That means screaming. Hope this helps, Ahmed! :)