The monsoon trough is a portion of the Intertropical Convergence Zone in the Western Pacific, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and northern hemispheres.
Westerly monsoon winds lie in its equatorward portion while easterly trade winds exist poleward of the trough. Right along its axis, heavy rains can be found which usher in the peak of a location's respective rainy season. As it passes poleward of a location, hot and dry conditions develop. The monsoon trough plays a role in creating many of the world's rainforests.
The term monsoon trough is most commonly used in monsoonal regions of the Western Pacific such as Asia and Australia. The migration of the ITCZ/monsoon trough into a landmass heralds the beginning of the annual rainy season during summer months. Depressions and tropical cyclones often form in the vicinity of the monsoon trough, with each capable of producing a year's worth of rainfall in a matter of days.