A software key is a licence, not a download
The code you buy does not contain the software. In almost every case you download the installer from the vendor and the key tells the vendor which licence you hold. That sounds like a technicality until something goes wrong, because it means two separate things can fail: the download can be fine while the licence is not, and a program that installs and runs today can stop being activated later.
It also means the vendor, not the store, is the party that decides whether your licence is valid. A store can sell you a code in good faith and the vendor can still refuse it, which is why the useful question about any software listing is what kind of licence the code represents rather than how cheap it is.
The four licence types, and why the price gaps exist
Retail is the licence sold to consumers. It is the most expensive, it can usually be moved to a different machine, and it is the one vendors support without argument.
OEM is sold to system builders to ship on new hardware. It is cheaper because it is tied to the first machine it activates on and is not intended to move. For a desktop you will keep for years this is often a reasonable buy; for a machine you expect to replace it is a licence you will pay for twice.
Volume licences are issued to organisations under an agreement, priced per seat at scale, and are not transferable to individuals. Keys from this pool are the usual explanation when a well-known program is listed at a tenth of its normal price. They frequently activate. They can also be deactivated centrally later, because the licence was never issued for the use it is being put to.
Subscription licences are rented rather than owned, and the code adds time to an account rather than granting a permanent right. What you are buying is months, and the terms of the subscription apply for as long as it runs.
What the listing has to tell you
The version and edition, precisely. Software names are close enough to each other that "Professional", "Professional Plus", "Standard" and "Home" get used interchangeably in listings when they are different products at different prices.
The platform. A Windows licence is not a Mac licence, and several vendors sell them as separate SKUs under one product name.
The device count. Consumer security and productivity software is commonly licensed for one, three or five devices, and a listing that omits the number is usually selling the one-device tier.
The term. "Lifetime" is a word that means very little in software: for a perpetual licence it is redundant, and for anything with a server component it is a claim about the vendor's future rather than about your rights. Where a listing says lifetime and the vendor sells only subscriptions, the listing is describing something the vendor does not offer.
Activation is not the end of the story
A key that activates has passed one check at one moment. Vendors revalidate, and licences obtained outside their intended channel can fail that later check months after purchase. This is the single most important difference between software keys and game keys: a revoked game disappears from a library, while a deactivated productivity licence can interrupt work you are in the middle of.
Where the software matters to you, weigh that against the saving. The gap between a grey-market licence and a retail one is often smaller than the cost of an afternoon spent reactivating a machine you needed that morning.
Before you buy
Confirm the edition, the platform, the device count and the term. Establish whether the licence is retail, OEM or subscription, and if the listing does not say, treat the omission as the answer. Redeem against an account you control and will keep, because for most vendors the account is where the licence lives.
Keep the purchase record. Vendor support will sometimes reissue or repair a licence when a genuine one has gone wrong, and the conversation is much shorter with an order number in front of you.
Get the installer from the vendor, not the seller
The code and the software travel separately, and only one of them should come from the store. Download the installer from the vendor's own site or the app store the vendor names, every time, even when a seller helpfully links a mirror or emails an attachment.
This is not a theoretical precaution. Repackaged installers for popular free and paid software are a standard distribution route for adware and worse, and a bundle that installs the real program alongside something else looks entirely normal while it does it. A legitimate seller has no reason to host the binary; the licence is what they sold you.
Where a vendor offers several download variants — offline installer, web installer, a specific architecture — the offline installer is usually the easier one to keep. Save it with the licence record, because vendors retire download links for older versions long before the licences stop being valid.
