What is the difference between sciatica pain and back pain?

Sciatica=down leg: Sciatica is pain due to compression of the sciatic nerve or its branches and is typically pain going down the buttock into the back of the leg (may be all the way to the knee). Back pain is in the back itself, and it could be from muscle strain/sprain, or from slipped discs and resulting spinal nerve compression. Back pain may radiate down the leg (front or side, or sometimes the back) as well.

Sciatica: Sciatic is due to compression of the nerves that leave the sciatic notch. Low back pain is the physical pain felt usually due to this.

Not Much: Sciatica can be just back pain alone, however typical pattern is back and leg pain.