together; abreast; side by side
Idiomatic phrase literally meaning 'lining up the bits (of horses)', used to describe people or things moving or acting together in parallel, often in competition or cooperation.
See also: 轡 (くつわ)
両社は轡を並べて新市場に挑んだ。
The two companies tackled the new market together, side by side.
They are advancing their research in parallel.