"Fear, uncertainty and doubt," shortened to "FUD," isn't a term exclusive to the bitcoin community.
Among bitcoiners, however, FUD is generally used to refer to anything, like negative press coverage or blog posts, that might dissuade people from joining the cause of cryptocurrency.
Otherwise, FUD can mean a number of other things, including the practice of hyping up a cryptocurrency you own to drive its price higher, or sowing discord among owners of another coin so you can drive the price down and buy it cheap. Sometimes, it just means "Facts U Dislike."