The Lowlands is not an official geographical or administrative area of the country. However, in normal usage it refers to those parts of Scotland not in the Highlands (or Gàidhealtachd). The boundary is usually considered to be a line between Stonehaven and Helensburgh (on the Firth of Clyde). The Lowlands lie south and east of the line. Note that some parts of the Lowlands (such as the Southern Uplands) are not physically 'low', and some areas indisputably in the Highlands (such as Islay) are low-lying.
In geological terms, the dividing line between Lowlands and Highlands is the Highland Boundary Fault. There was also a legally defined Highland Line in the post-Culloden years as part of measures aimed at suppressing Gaelic culture.
For other purposes, the boundary varies, but if the Boundary Fault is used, then the traditional Scottish counties entirely in the Lowlands are Ayrshire, Berwickshire, Clackmannanshire, Dumfriesshire, East Lothian, Fife, Kinross-shire, Kirkcudbrightshire, Lanarkshire, Mid-Lothian, Peeblesshire, Renfrewshire, Roxburghshire, Selkirkshire, West Lothian and Wigtownshire.
Geographically, Scotland is divided into three distinct areas: the Highlands, the Central plain (Central Belt), and the Southern Uplands. The Lowlands cover roughly the latter two. The northeast plain is also "low-land", both geographically and culturally, but in some contexts may be grouped together with the Highlands.
The southernmost counties of Scotland, nearest the border with England, are also known as the Borders. They are sometimes considered separately to the rest of the Lowlands. Many ancestors of the Scotch-Irish, as they are known in the United States, or Ulster-Scots, originated from the lowlands and borders region before migrating to the Ulster Plantation in the 17th century and later the American frontier, many prior to the American Revolution.
- East Lothian was known as Haddingtonshire until 1921.
- Mid-Lothian was known as Edinburghshire until 1921.
- West Lothian was known as Linlithgowshire until 1921.