Nelson immediately gave out instructions after he formally introduced the Magic circle. He said that the magic circle is called Training Summoning Circle, TSC its abbreviation. Though it is jokingly nicknamed a "Temporary Circle" by junior summoners. As for why it was called so, it lied on its function.
TSC simply opens a temporary channel to call summons to its chanter. Meaning most of its summons don't last long, either due to the summoner finding a better magic circle and summon. Or the summon wishes not to stay after its purpose is met. The circle itself is very limited. It can't call powerful summons as one of its runes restricts and repels them. Most summoner isn't satisfied with the variety this magic circle calls, so the contract done between the summon and summoner is only temporary. So with its current characteristic, the magic circle really lived with its nickname "Temporary Circle."
