Only top scored, non community-wiki answers of a minimum length are eligible
As explained in Todd Trimble's comment, It's Community Wiki. You don't gain or lose reputation points when a thread is in CW. Further reading: What are “Community Wiki” posts?
It's cleverly hidden under the Stack Exchange logo drop-down on the right-hand side of the top bar (NOT the one on the left-hand side of the top bar): Alternately, you can just type "meta." in the ...