In this paper, a new definition of the monsoon in the lower troposphere has been presented. Upon analysing the global cli-matic data of GFDL, it is found that the monthly mean horizontal wind system in the lower troposphere can be considered as the linear combination of two parts. The first part is the annual mean wind system which represents the atmospheric res-ponse to the orographically induced large scale statioary disturbances. The second part is the departure wind (monthly mean wind minus annual mean wind) which represents the atmos-pheric response to the heating contrast between oceans oceans and continents’ including large scale orography, i.e. the monsoon. Unlike classical definition, the above defined monsoon wind systems have clear physical interpretation, and have been conveniently used in the meteorological analysis.