Term commonly used in N. Ireland to describe Catholics who desire a united Ireland and ram there tri-colour flag (strange how a person born within the UK would sport the flag of another country and claim it as there own) down other peoples throat. They however never have any trouble or much to say when it comes time to collect their state benefits in sterling sporting the image of Queen Elizabeth 2, which they would not get down south or in the unlikely event of a united Ireland.
This is not a term of endearment and infact derives from an irish word, so it's ironic that Protestants use a foreign (Irish) word against Catholics.
See also taig , Sinead O'Connor, Jerry Adams
"Fuck off back the south ya dirty, fenian, scummy, bastard"
"1st step toward a united Ireland is when those fenians give up there benefit books and stop accepting the queens' money for nothing"