There's a real line. Adaptive reuse means the building's purpose changes, office to residential, warehouse to apartments, church to offices. The practical marker is that the building's legal use changes and it needs a new certificate of occupancy for a different occupancy classification. That is what pulls in new code requirements for egress, fire rating, sprinklers, accessibility, and often a zoning approval, and it's why conversion construction costs so much more than a refresh.
Your two other examples are not adaptive reuse in that strict sense. New lobby finishes and a gym in an office building that stays an office building is repositioning, sometimes called a value add renovation. The use never changed. A grocery space becoming a gym is a tenant change inside the same broad commercial use, so it may need a permit for the fit out and possibly a use permit depending on the local zoning table, and the building is still a retail center. Brokers do stretch the term because it sounds current, so when you read it, ask what the certificate of occupancy said before and after.
Since you work in zoning, the part that surprises people coming from the land side is how much of the cost sits in code compliance rather than finishes. Changing occupancy classification can trigger full sprinklering, a second stair, structural upgrades, and accessibility work on a building that was legally fine the day before. Which of those apply depends on your state's adopted code and the local existing building provisions, so that's a conversation with the building official, not a code book you buy once.
