I think they're often made from woods like teak that will hold up to moisture, and they seem to have light brown leather bellows, although I don't quite know what purpose that serves. Maybe the leather is cured in a different way for the climate, or perhaps it is a different type of leather. They seem popular among collectors.
Just got an old Japanese 1/2 plate camera (have not received it yet) and the wood looks to be other than cherrywood. Has black leather bellows, though (and no mosquito netting). Just trying to determine whatever I can about it. Will post on the vintage camera area when I receive it.
It simply means a camera that is designed to be unusually resistant to heat and humidity. The classic examples were reflex and small field cameras that were normally leather covered, but were left as bare wood in their 'tropical' incarnation. There may also be some extra brass binding, and the camera may be made of more, smaller pieces of wood.
To a large extent, it's a marketing term. The best cameras were OK for the tropics anyway; the cheaper ones might warp even if they were sold as 'tropical'.