Shiplap describes an overlapping weather-shedding profile. Tongue and groove describes how boards interlock. A board can use both ideas, so retailer category names are not always a clean either-or comparison.
Ask for finished thickness
The profile does not tell you the finished board thickness, timber grade, frame spacing or treatment. Those details affect how the wall behaves and deserve their own line in a comparison table.
Check the face you are comparing
Nominal and finished dimensions can differ after machining. Ask whether a quoted thickness is nominal or finished and keep like-for-like figures together.
Profile is only one part of weather resistance
Good detailing at corners, openings, the roof edge and the base matters. So do maintenance access and timely treatment. Do not let a familiar cladding label distract from an unspecified floor or roof.