What we mean depends on the context we are discussing. There isn't a single "meaning" for the term. But it is certainly NOT true that an electron, once observed, will remain in its observed position. I am extremely dubious that you "heard" that somewhere. In general, you can understand a bit of the reasoning with regard to the way subatomic physics works. All particles carry momentum. In order to observe an electron, you have to interact with it (by definition). So, what are you going to interact with it with?? Right, a particle. And that particle can transfer (or take) some momentum from the electron during the interaction. Which means that the electron will likely move because of the interaction. QM has a lot of non-intuitive characteristics. One of them is that the (macroscopic) concept of "position" is of marginal use for subatomic physics. Distance between particles is far more important, but because of superposition, location is not well defined (on a subatomic scale). This isn't only true with subatomic particles. Think about (as one example) a lake. What is its "position"? Well, we can (more or less) pin-point the center of the lake, but what about the shore? Can we draw a razor sharp line (or curve) which has lake/water on one side of it and ground/sand/soil/rock on the other? No. It will depend on wind, waves, rain, evaporation, tides, etc. The best you can do it locate a line beyond which the lake usually doesn't exist (high water mark). This is arbitrary and often not even accurate. Let's think about that a bit more: if we can't "really" define the (exact) border, then can we really define the lake's center? So, do we really know what we mean when we talk about the lake's position? Well, for practical purposes we can. What we mean by "position" of the lake depends on the discussion's context. It's more important that we understand what we mean by a lake's position than it is to understand a subatomic particle's. Why? because one is far more useful than the other. Teachers like to contrast the differences between QM and Classical physics by high-lighting the differences. In fact, many of the "strange" things of QM have analogs in our macroscopic world. What is the sound of one hand clapping? Is that a meaningful question? Does a (single) hand have a property called clapping?