To continue with our mind, remember that in Tibetan you could build new words using the syllables pa, po, ma, mo. If you add pa to sems, you get sems pa, something like a 'mind thingie'. What this 'mind thingie' really is, that's a hard word to translate. One way to translate is the movement of the mind. Another translation term is to think, reflect, motivation, intention, or even something like the directionality of the mind!
To really understand this, it's good to have a basic primer concerning the mind. In Abhidharma-kosha, the mind is described as a continious flow of pieces of thought, there are 65000 of these discrete movements of the mind in about a fingersnap. That's sems pa, or this translated back to Tibetan, de ni sems pa.