Beyond the literal meaning ('person walking past'), 过路人 is a frequent metaphor in songs and breakup lyrics for someone who used to matter but is no longer significant - 'just a passer-by in my life.'
memory
过 (pass) + 路 (road) + 人 (person) = 'road-passing person.' The structure is the same as 行人 (pedestrian) but more specific to people walking past.
