What is a "free baron" ?

[Ledganteast]

Does anyone know what this term means?

My 4th G.Grandfather [b.1788-d.1859] refers to himself as a "Free Baron of Dover"?

I can't seem to find the term anywhere offline or online.

[Guy Etchells]

It means he only owed allegiance and service to the king.
Cheers
Guy