This is a clear definition of DRM Free, frazap, and it is the one I
go by DRM is usually tied to a client (like Steam or Origin).
Once you buy the game and install it with a key, the game gets tied to your account with that client and that key cannot be used to install it on any other accounts.
A game that is DRM-Free is a game that does not have any DRM scheme. It can be installed as many times on as many different machines as you want and is not tied to any account anywhere. The idea is that the publisher of that game trusts you, as an honest person, to not distribute their game en-masse. It's effectively the logical extreme of the old Shareware model.
That is someone's definition on DRM-free, and I basically agree. But I don't mind using Steam as what can be called a download/install client, as long as the game once installed is not at all tied to the Steam account or the very computer it was first installed on. I'm just trying to say that some games aren't. One example is Contradiction. I bought it on Humble store, which gave me one DRM-free (in the pure sense) version and one Steam key for the game. The DRM-free version turned out to an old version so I installed the Steam one. Once installed you can shut down, even uninstall, Steam and move the folder containing the game to another computer. It still works. Giving me the exact same result as with the version downloaded directly from Humble store (only, in this case, bug free).
Very few games on Steam are like this though and I haven't tried moving the new Barrow Hill installation to another computer. But once installed at least it does not need the Steam client to run.