When a bone is partly out of its usual place in a joint.
Subluxation is a word used in medicine, especially in chiropractic care.
Examples:
The subluxation in my back is causing pain.
The doctor said I have a subluxation in my shoulder.
She went to the chiropractor to fix her subluxation.
The subluxation in my spine is making me feel wonky.
The subluxation in my neck feels like a big problem.
The subluxation in my knee is making it hard to walk.