NEMA 15 is the standard electrical outlet found in American buildings for 120VAC wiring. It comes in several styles, but the most common one is two parallel slots, one (the neutral) slightly wider than the other, and a ground slot centered beneath them. On those outlets rated for higher amperage, the slot on the left (neutral) looks like a sideways T; there are special plugs that can only connect to those. I consider them unsafe because they allow for easy contact with the hot blade while plugging them in. IEC 320 is safer in this regard, since it has a shield.