“Rank-and-file” is originally a military term. It refers to the lower “ranks” of soldiers, who literally stand in lines or “files”. These soldiers have a different set of interests in preserving their lives than the officers or “brass” who prosecute the wars on behalf of the ruling elite.
Rank-and-file committees are of, by and for the rank-and-file workers, who have a different set of interests in preserving their lives than management, the bosses, the politicians, and the trade union apparatus, who send workers to die while defending the profits of the ruling elite.