Why are "tropical waves" referred to as "Invest 95" , "Invest 96," etc.?

Question

Here's an example.

What exactly does "Invest" mean in this context?

http://www.wunderground.com/tropical/tracking/at200894_model.html

Answer 1

The hurricane center gives an area they are investigating but is not yet a depression a number.  That is so they can run the hurricane models on it for forecasting purposes.