Claptrap is defined by Webster's Dictionary as "pretentious nonsense." It is used to describe pretentious but insincere or empty language. It can also refer to any nonsensical rants that purport to argue a valid point.
The origins of the term are in the theater, where it originally referred to any device intended to elicit applause (to trap a clap).
Claptrap is often used preceded by a qualifier to associate it with a particular standpoint, as in the phrases "liberal claptrap," "atheist claptrap," "neoconservative claptrap," etc. In some circumstances this can be a useful shorthand to clarify why the statement in question is nonsense, in others it is merely an attempt to condemn the statement as invalid without going to the effort of any in-depth analysis.