what defines a commercial property

[Gaston Barua]

Hello BP Guros!

I am new to the RE Investing world and am doing some research on buying my first investment property. I am a little confused however by what a "Unit" is defined as in terms of real estate. Is a "Unit" a single bedroom? Or is it each individual housing space in say a duplex, triplex, or fourplex? I have heard the broad term used in both cases. Also, at what point does a property become commercial? How many "Units" would be necessary? 

Thank you all in advance!