I find it interesting that the community surrounding a DRM free platform is so mislead about what DRM is. Since our medium is so polluted with various forms of "management" that we bicker over terminology and can no longer decide on common ground for the definition, let's simply look elsewhere to define our common ground: Software.
Here's some software: https://mirrors.kernel.org/gnu
Notice the distinct lack of CD keys, "copy protection", online checks, or otherwise any means of self limiting code execution.
Here's another example of software: http://xpadder.com/?lang=english&country=US
This one is hidden behind a paywall. It's not free. Notice the distinct lack of CD keys, "copy protection", online checks, or otherwise any means of self limiting code execution.
It really is as simple as that.
A lot of the discussion in these GoG threads boil down to being pedantic, which I don't find helpful or otherwise productive. I'd like to specifically address the notion that "copy protection/serials aren't DRM". I don't find this distinction meaningful. These are two means of self limiting code execution. While you might consider them different in that "copy protection/serials" are older methods to curb piracy, and "DRM" is a newer method to curb piracy, they're both a means to the same end. Modern "DRM" is simply the logical progression of "copy protection"- it's the same idea, just evolved to deal with an evolving technological landscape (and evolved in ever more complex forms to deal with users circumventing it). Pointing out such minute pedantic distinctions in these discussions is a red herring: it's sort of like saying that a sword isn't a weapon because it can't shoot bullets, and all our weapons today shoot bullets. (I know, the analogy isn't perfect, try to meet me halfway here :)
I'm quoting timppu here, because, despite my disagreement re: product key, I find his response to be the most lucid and constructive. It really highlights that in today's landscape, some "self limiting code execution" in certain aspects of the game is not only acceptable, but downright beneficial to the community surrounding the game. His response dispels the "all or nothing" false dichotomy that often pervades these discussions. Well done.
DRM is copyright protection. One of the oldest DRM protection methods is a product key.
DRM is Digital Rights Management, ways trying to manage (restrict) your usage of a product after the purchase.
A product key in itself is not DRM unless it is somehow e.g. authenticated online before you can use the product. If it is not, then it is in no way restricting how, where or when you can use the product.
Some GOG games can be considered to have multiplayer DRM, requiring even an online account to play multiplayer online. So yes you should consider the DRM-freeness of GOG games to pertain to the single-player part of a game (and yes maybe GOG should also clarify that somewhere, if not for other reason but to stop these same discussions popping up every few weeks). With multiplayer part it varies; some games may have an option for DRM-free multiplayer as well, for some the multiplayer part has been made inert in the GOG version (because the multiplayer would work only e.g. in Steam) etc.
I guess there is a general consensus that a game can be considered DRM-free as long as its single-player part doesn't require online authentication or other restrictions to playing it. For instance, these Steam games
are considered DRM-free even though their multiplayer part requires a Steam account, it is only the single-player part that is DRM-free. Also I am pretty sure e.g. Humble Bundle/Store is marketing DRM-free games where it pertains only to the single-player part.
I personally even prefer DRM in online multiplayer
because it is the only feasible way to ban cheaters from destroying other people's fun. So DRM in online multiplayer even benefits me as a gamer. I am not against the game having also other (DRM-free?) options for multiplayer as well, like local co-op, LAN play, direct IP and whatever there are...
Single-player, I want DRM-free, there I don't have to care about other people possibly ruining my fun with cheating. There I care only that I can run the game even if the store/service from where I bought the game is closed down or inaccessible. There I don't see how DRM would benefit me (and no, requiring an online account for optional features like cloud saving, achievements tracking, leaderboards etc. is not DRM, as "optional DRM" is an oxymoron).