Brewer's: Borough English
is where the youngest son inherits instead of the eldest. It is of Saxon origin, and is so called to distinguish it from the Norman custom.
“The custom of Borough English abounds in Kent, Sussex, Surrey, the neighbourhood of London, and Somerset. In the Midlands it is rare, and north of the Humber ... it does not seem to occur.” —F. Pollock: Macmillan's Magazine, xlvi. (1882).