Someone who identifies with or is sympathetic to the aims or ideology of a political movement or organization, but is not a formal or full member of it. Used especially in the 1950s in reference to those suspected of being communist sympathizers. In my grandfather's day, if someone accused you of being a fellow traveler, it was often to derail your career completely. Despite having a mark against him as a "fellow traveler," he still managed to remain at the Hollywood elite.

One who speaks authoritatively about traveling despite not traveling often. Don't let him discourage you when he's just an armchair traveler who's never been out of the country!