What characterizes the area between the two tropics?
Well in between the two tropics is the equator.
Hence the tropics being very hot and humid through all seasons. The area between the tropics is also, in general, very forested with a lot on animal diversity.
The weather between the tropics is also extreme in many cases, ranging from stagnant calms to erratic thunderstorms. This weather is caused, in part, by the trade winds from either hemisphere as they converge. Sailors refer to this area as the doldrums .
To learn more about what the tropics are, visit Intertropical Zones