molly-guard /mol'ee-gard/ n. [University of Illinois] A shield to prevent tripping of some Big Red Switch by clumsy or ignorant hands. Originally used of the plexiglass covers improvised for the BRS on an IBM 4341 after a programmer's toddler daughter (named Molly) frobbed it twice in one day. Later generalized to covers over stop/reset switches on disk drives and networking equipment. In hardware catalogues, you'll see the much less interesting description "guarded button".
From the Hackers Lexicon
Not having very much content yet, I thought I'd bung this quote from the Hackers Lexicon in. Something I'm likely to do rather often.