Nah, Wikipedia. It must be true! Wikipedia and Facebook are the only trustworthy sites on the interwebs.Also by that definition anything above a 2x4 is a plank, but I guarantee if I went to lowes and asked where their 2x6 planks were I’d get some strange looks.
Plus I could just find a single source for that definition so I feel like you are cherry picking your source to prove your point.