This term can be used both literally, to describe someone who lacks physical flexibility, and figuratively, to describe someone who is unwilling to change their mind or adapt to new situations.
Here are some other terms that could be used, depending on the context:
* Stiff
* Rigid
* Unbending
* Unyielding
* Inflexible
* Uncompromising (figurative)
* Dogmatic (figurative)