Quick answer: Scooting almost always means anal gland discomfort — the sacs on either side of the anus are full, impacted, or irritated and your dog is trying to relieve the pressure by dragging.
Anal glands are small secretory sacs that normally empty during bowel movements. In some dogs they don't empty properly, causing fullness and discomfort. Impacted or infected glands need manual expression by a vet or groomer — this is a common, quick, and inexpensive procedure.
Less commonly, scooting is caused by intestinal worms (especially tapeworms — check for small rice-like segments near the anus), allergies causing perianal itching, or irritation after grooming or bathing. If anal gland expression doesn't resolve the scooting, these should be investigated.
Persistent scooting, visible swelling near the anus, discharge, or a strong fishy smell needs vet attention. Impacted anal glands can develop into painful abscesses if left untreated for too long. Don't delay if you notice swelling or discharge.
Scooting is almost always anal glands. Expression by a vet or groomer resolves it quickly. If it's a recurring problem, a higher-fiber diet often helps with natural expression during bowel movements.