Younger is a Scottish convention, style of address, or description traditionally used by the heir apparent to:
A current laird (owner of a substantial and landed estate in Scotland)
Someone whose name includes a territorial designation (i.e. a family who were previously lairds but who are no longer – this applies mainly to armigerous families who had a territorial designation which formed part of their name. Their arms being registered with the inclusion of the territorial designation, having become landless, still retain the full name – including the territorial designation – pertaining to the Grant of Arms)
A Scottish chieftainship (the head of a cadet branch of a clan which has a chief)
The style of using the term "Younger" applies equally to a woman who is heir in her own right as to a man. The style of "Younger" is neither a title of nobility nor a peerage and does not carry voting rights either in the Parliament of Scotland or the Kingdom of England. The abbreviation of Younger is Yr. The wife of such an heir may adopt this style also.
When a person bearing this suffix becomes the laird or Baron in their own right or succeeds to the arms of a now landless family or inherits the chieftainship of a cadet branch or the chiefship of the clan, they then drop the suffix and the next heir apparent may add the style to their name.
^Ruling of the Court of the Lord Lyon (26 February 1943, Vol. IV, page 26): "With regard to the words 'untitled nobility' employed in certain recent birthbrieves in relation to the (Minor) Baronage of Scotland, Finds and Declares that the (Minor) Barons of Scotland are, and have been both in this nobiliary Court and in the Court of Session recognised as a 'titled nobility' and that the estait of the Baronage (i.e. Barones Minores) are of the ancient Feudal Nobility of Scotland".