I don't think there's a single standard. I've seen publications define their own, but as for there being some magic moment when you are Intermediate instead of Beginner, or Piquant instead of Tangy, or whatsumever, no. I had one student panic because the very plain sock pattern we were going to use said Intermediate. She did fine, but it was rough convincing her she would.
In general, if you can look at a pattern, understand it, and decide whether you'd like it, you can handle it. I had someone try to tell me I couldn't knit a certain shawl because I didn't have a Master Knitter certificate. Heh! the yarn doesn't know that.
Also, there will be times in your life when the easy/medium/hard labels may be handy. We're just coming off a mean viral bronchitis that has left us all feeling kinda stupid. I sat here one day with yarn and needles and a simple pattern (my own, at that!)...and I couldn't focus enough to do it. For some people, knitting lace is so absorbing that it distracts them from tension; for others, it adds more when they seriously don't need it. Some people can't knit in waiting rooms and some have to. If you know your own stress level and how knitting affects it, you can pick a project to suit.