A double sconce is a wall mounted light with two light sources instead of one.
Think of it as a single backplate on the wall with two arms or two shades extending from it. Sometimes both lights face up. Sometimes they face down. Sometimes one goes each way. The layout depends on the design, but the idea is simple. More light from one spot.
You will often see double sconces in bathrooms, especially beside or above wider mirrors. The extra bulb helps spread light more evenly across your face, which makes everyday tasks a little easier. They also work well in hallways or along larger walls where a single sconce might look too small.
There is also a visual difference. A double sconce takes up more horizontal space, so it can anchor a wall better. On a tall or wide wall, that added width feels balanced rather than sparse.
It is not complicated. It is just a sconce that does a bit more.
Two light sources. One fixture. Slightly stronger presence.