Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
You have to double-check with Costco to find out what you purchased, exactly.
Full versions of Office that you install on a PC or Mac, no matter if you have a one-time payment (perpetual) license (such as Office Home & Business 2024) or a subscription (such as Microsoft 365 Personal), are always installed locally on your computer.
Terminology is sometimes a bit confusing. Sometimes, "Microsoft 365" means both subscriptions and perpetual (one-time payment) licenses. More specific would be to speak of "Microsoft 365 and Office" when referring to both product categories.