Habituation is a real psychological process and is a bit different than "acceptance", and it does not apply to just tinnitus. It basically means that conscious response to a stimulus is diminished after repeated exposure, as your brain begins to understand that it is unimportant.
For example, when you've been walking around all day, you don't constantly consciously perceive the feeling of your socks on your feet. (You probably do now that I mentioned it.) Your brain tunes out the sensation as unimportant, probably almost immediately after you put them on. You can feel your socks if you think about it, or maybe if you notice something strange like one of them has developed a hole worn in, but normally it is completely out of your realm of thought. This is habituation at work.
You also habituate to sounds. Ambient noises like your AC unit running, the sound of your laptop fan whirring away, or the sound your car engine is making while you're on a long drive could be things that you stop perceiving after a while. People don't go nuts over these sounds. Depending on your sensitivity, you could possibly habituate to non-constant sounds, like perhaps the sound of planes flying overhead if that is something that happens frequently in your location (as in, you totally wouldn't notice that a plane has flown by unless something out of the ordinary happens to draw your attention to it).
Tinnitus is tougher because it is normally a rather unpleasant sound. I don't think that you can achieve habituation without first achieving "acceptance" because you have to be able to experience tinnitus without anxiety before your brain will allow you to tune it out. CBT can help with this. For some people, habituation comes quickly and easily (these people won't be complaining on tinnitus online forums), and for some people it takes a while to get there. If/when you habituate, it becomes just another piece of background noise that your mind can easily tune out, but is never actually completely gone.