Is it passers-by or passers-by?

Before the mid-sixteenth century, the now-obsolete passager had the same meaning. Today, passer-by is a fairly straightforward word ("one who passes by"); its only slightly confusing aspect being the plural form, which is passers-by.

What is mean by passer-by?

A passer-by is a person who is walking past someone or something. A passer-by described what he saw moments after the car bomb had exploded. I went and sat in a cafe and watched the passers-by. Synonyms: bystander, witness, observer, viewer More Synonyms of passer-by.