In Scotland before 1603 there were only two kinds of peerage title commonly held. Earldoms were originally territorial - in other words the earl of Ross held most of Ross from the king and was responsible to him for administration and law and order in the area. There were 7 of these great earldoms in the 13th and 14th centuries but the number increased later. By about 1450 there were also lords of parliament - just called lord X - who, along with the earls sat in parliament (in one chamber with the churchmen and representatives of the burghs) but had lesser responsibilities. Apart from the royal family there were no dukes in Scotland before 1603. After the union of crowns in 1603 the systems became less clear-cut and dukes, marquises and viscounts were also created in Scotland. (Dukes, marquises and earls usually have several minor titles, one of which is chosen by the eldest son as a courtesy title.) There were knights (called Sir) but the title was not (and still is not) hereditary. Baronets (also called Sir but a hereditary title) were created in Scotland form 1625 - Sir Hector Munro of Foulis was made a baronet in 1634, but because the baronetcy went to male heirs only, the father of the present chief followed his mother in the estates, but the title went to a cousin.

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.