* Definition of "Professor": The title "Professor" has varying meanings across countries and institutions. Some countries use it more broadly than others. Some institutions might use different titles (Associate Professor, Assistant Professor, Lecturer) for faculty who perform similar roles.
* Data Collection Challenges: There's no central, global database tracking every university and college, let alone the number of professors at each. Information is scattered across countless institutions worldwide.
* Constantly Changing Numbers: The number of professors is constantly fluctuating due to retirements, appointments, and changes in university sizes.
While a precise number is impossible to obtain, a very rough estimate would likely be in the millions. However, this is a very broad and unreliable figure.