for most things, "guest" means "anyone you want, as long as they are with you".
For example, the member benefit to getting into the DVC Lounge, Top of the World, etc. are "For the member and 3 guests"...meaning: One person shows their card, and 3 other people that are with that person can also get in...no questions asked. A lot of the dining discounts work this way well: "for the member and 3 guests"...basically, up to 4 meals will be discounted, as long as one of those meals is for a DVC member...the other 3 doesn't matter.
Some discounts are STRICTLY for the official card-carrying DVC member only: Merchandise discounts
Some discounts are for the DVC member and their immediate family only (spouse/children living in the same house): Annual Pass and most other ticket discounts.