It referres to the amount of those kinds of pins that you have combined. If you have 2 magic pins of the same type, you can combine them to make the pin last longer, and have a shorter wait time between using the pin again.
You can have up to 5 pins combined together.
I'm sure this must already be posted somewhere, but I haven't found it....
How do you get multiple pins? Can it be done without trading? e.g. Can you win more times at pirates for another Invisibility pin? If so, how? I've could swear I've won at least another 20 times at level 3 without getting another pin. Do you have to start over & win 10 level one followed by 10 at level two etc?