What is the key difference between work centers $($job shop$)$ and manufacturing cells?

$$ Work centers are dedicated to the production of a specific part or parts family

$$ A work center contains similar machines identified by their operation, whereas manufacturing cells have dissimilar machines identified by similar product families.

$$ Manufacturing cells are areas where similar machine types are grouped together $($e$.$g$.,$ the "grinding" cell$).$

$$ No practical difference; "work center" is a term more common to the service industry, and "manufacturing cell" is used in tangible goods manufacturing. Both mean essentially the same thing.

Work centers have employees, but no machines, and manufacturing cells have machines, but no employees.