The term maritime tropical refers to an air mass's humidity and temperature. Maritime sounds like "marine". Marine is a term that relates to the sea. Thus, a maritime tropical air mass is going to originate near the sea. This is going to cause the air mass to be somewhat humid. The term "tropical" is going to imply that the air mass is within a warm climate. Thus "maritime tropical" refers to a warm, humid air mass.
There are four types of air masses They are each classified by a series of two words. The first word refers to its humidity and can be either maritime (moist) or continental (over land, and, therefore, dry). The second word refers to its temperature and can be either polar (cold) or tropical (warm).