I want to know what is the difference between chronic back pain and sciatica?

Several: Chronic when referred to pain is pain lasting longer than 3 months. Back pain can have multiple causes and may or may not be associated with any pain that will travel down a leg past the knee which would be termed a sciatica. Sciatica most commonly occurs due to disc herniation compressing one or more nerves that form the sciatic nerve in the leg. There can be other causes of sciatica.

Back and leg pain: Generally sciatica implies leg pain, which can occur with or without back pain. At a medical level, we concern ourselves with the presence or absence of nerve root irritation at the spinal level which can lead to leg pain with or without neurologic injury. Back pain itself may be secondary to injuries of the joints, ligaments or disc.

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