What is the difference between baclofin and flexeril?

Baclofen and Flexeril are both muscle relaxants but work in different ways so are prescribed for different symptoms.

Flexeril is used for relief of muscle spasm associated with acute, painful musculoskeletal conditions.

Baclofen is used for the alleviation of signs and symptoms of spasticity resulting from multiple sclerosis and partial spinal cord injuries.

See these links for more detailed information:
https://www.drugs.com/pro/flexeril.html
https://www.drugs.com/pro/baclofen.html
https://www.drugs.com/compare/baclofen-vs-flexeril