I personally think this is a conspiracy on the part of mainstream tent makers to make their tents appear lighter than they are. It seems that every one has a slightly different definition.

Most "cottage" manufacturers, such as Tarptent and ZPacks, are at pains to disclose the actual weight of the tent, not just a total but the components, including stuff sacks, stakes, etc. That's one of the many reasons I prefer to buy from them.

IMHO, a footprint is not necessary; it's just a marketing gimmick. I haven't used one for years, and for the past 9 years my tent had a lightweight silnylon floor. (I never used one with my old 1980's tent, either.) Never any problem, even with a fairly large dog in residence.