I guess that it means that you can use it universally.
On objectcreation you specify what type you want to use e.g.
CARTYRE <int> tire;
And then all occurrences of T will be replaced by the specified type.
In the car.h file you'll see CARDYNAMICS <double> dynamics, which means that for all of the car classes "double" gets substituted for T. I did it this way in case I wanted to try using a 32-bit float instead of a 64-bit double.