BEM

noun3

1. •
   (slang) A stock character in science fiction; a grotesque creature, often an extraterrestrial, that menaces the protagonists.

   • Incidentally, Mr. Bergey, the BEM's on your latest smear have extremely jovial expressions on their pans to be as tough a bunch of eggs as Friend made them out. — 1940
2. •
   Initialism of British Empire Medal.

   • He felt secure and encouraged, had visions of a BEM and made the first payment on a Morris Minor. — 1953
3. •
   Initialism of block, element, modifier, a convention for authoring CSS.