I went to the battle subway today, and saw two new teams to me that I don't understand what it means. NU and LC
They stand for NeverUsed and LitteCup. They are tiers in the competitive world, check out Smogon for all the competitive info. Other tiers in OverUsed, UnderUsed, RarelyUsed, and Ubers.
NU and LC are both tiers used in conpetitive battling.
NU = Neverused
LC = Little Cup
NU is the lowest tier of all, where all the less decent Pokemon are placed. LC is more of a standalone tier; basically, only Pokemon that are in their first evolution form are allowed to participate. LC has many different rules compared to the other tiers as well.