Alba is the Scottish Gaelic name for Scotland. Historically, the term referred to Britain as a whole and is ultimately based on the Indo-European root for "white." I would guess the white chalk cliffs had something to do with it, plus when viewed from the north coast of France, or the sea, the island is often under a layer of white cloud. Scottish Gaelic speakers used it as the name given to the former kingdom of the Picts around the reign of king Causantin mac Aeda (Constantine II) from 943–952. The region Breadalbane (Bràghad Albann, the upper part of Alba) also takes its name from it.
There is no precise Gaelic equivalent for the English terminology 'Kingdom of Alba' since the Gaelic term Rìoghachd na h-Alba means Kingdom of Scotland. English scholars adopted the Gaelic name Alba to refer to a political period in Scottish history that existed between 900 and 1286.
The territory of Alba extended from Loch Ness south to the firths of Clyde and Forth while The Hebrides, Orkneys and Shetlands, together with much of the mainland north of Loch Ness, remained under Viking control. Southwest Scotland (the Kingdom of Strathclyde) suffered under the same Norwegian Vikings who settled in Dublin. In the southeast, Lothian, once part of the Anglo-Saxon kingdom of Northumbria, lay under the control of the Danish Vikings who settled in York
The people of this period in Alba were mostly Pictish-Gaels, or later Pictish-Gaels and Scoto-Norman, and markedly different to the period of the Stuarts, when the elite of the kingdom were mostly speakers of Middle English, which later evolved into Lowland Scots.