What is Lord Advocate?

Legal Definition
Her Majesty's Advocate, known as the Lord Advocate (Scottish Gaelic: Morair Tagraidh, Scots: Laird Advocat), is the chief legal officer of the Scottish Government and the Crown in Scotland for both civil and criminal matters that fall within the devolved powers of the Scottish Parliament. He or she is the chief public prosecutor for Scotland and all prosecutions on indictment are conducted by the Crown Office and Procurator Fiscal Service, nominally in the Lord Advocate's name.

The officeholder is one of the Great Officers of State of Scotland. The current Lord Advocate is The Rt Hon. James Wolffe, QC.
-- Wikipedia
Legal Definition
The principal crown lawyer in Scotland, and one of the great officers of state of Scotland. It is his duty to act as public prosecutor; but private individuals injured may prosecute upon obtaining his concurrence. He is assisted by a solicitor general and four junior counsel, termed "advo-cates-depute." He has the power of appearing is public prosecutor in any court in Scotland, where any person can be tried for an. offence, or in any action where the crown is interested. Wharton.
-- Black's Law Dictionary
Legal Definition
The chief public prosecutor of Scotland. 2 Alis. Crim. Pr. 84.
-- Black's Law Dictionary
Legal Definition
(Scotch) The chief prosecutor.
-- Ballentine's Law Dictionary