INFORMATION SHEET No. 16
Peers and Barons
In Scotland before 1603 there were only two kinds of peerage title commonly held.
Earldoms were originally territorial -
Barons in Scotland were not peers in the sense that they did not automatically sit in parliament. They got their designation (not strictly a title and they were not called lord) when their lands were made into a recognised unit by the king (the official phrase was "erected into a barony") and they were given limited powers of administration and legal responsibilities (the latter of which they held until 1747) over the unit. Foulis was made into a barony about 1550 (the charter has not survived) so strictly speaking Robert Mor (d 1588) was the first baron of Foulis although his ancestors had held the lands from the earls of Ross and then from the king for centuries before that date.
Confusingly in more recent times baron has become a peerage title in Britain and the holder of these titles are called lord (or lady), but this has nothing to do with the older Scottish version.
Also in Scotland it was the custom for a landowner without other title to use the name of his estate as part of his name (what is called a territorial designation). Thus long before 1550 the chief was known as Munro of Foulis and some of his family used their estates also e.g. Munro of Milton, of Katewell, of Obsdale etc.