Commuter Category is defined rigorously, 

<https://www.law.cornell.edu/cfr/text/14/23.3>

But I was unable to find an equivalent definition for Transport Category in the regulations (not Wikipedia or the FAA website, haha). Nor was I able to find anything like "if requirements not met for Commuter, then the vehicle is in Transport Category." 

Could somebody point me in the right direction?

Thank you.