If you are aware that you are dreaming during the dream, it is a true lucid whether you have any control over it or not. What I would call a “semi-lucid” is a dream where I'm vaguely aware on some level that what I'm currently experiencing isn't waking life but without it quite reaching full conscious realization.

I'm not sure I completely understand the OP question, either, but it is certainly possible to slip in and out of lucidity during a dream. You can realize you're dreaming for a bit, then get too focused or distracted on something else and forget, becoming non-lucid again.