Authorizing 5 computers

iTunes allows you to authorize up to 5 computers per account for purchases that are made. What is considered a "computer" to iTunes.

For example, I have an iPhone, an iPad, an iMac, a MacBook, a PC laptop and a PC Desktop. Is the iPhone considered a "computer"? What about the iPad?

I am fairly certain that the iMac, the MacBook and the 2 PC's would be considered computers.

Does anyone know the answer to this for certain (no guessing please).

Thanks