The Picts were an ancient people who lived in what is today called Scotland.
It is written that the Scottish people are a mix of a number of different people; the Picts being one of them.
People of Pictish Descent
Although I do not know if this is a hard fast rules (although it could be), I've been told that all family names that end in "son" are Pictish family names. For example...
I have been told that my father's mother's mother was born a Dickson. And if that is the case, and the rule about names ending in "son" being Pictish is true, then I am of Pictish Descent.
I do not know if all Pictish family names end in "son" though. (There may be other forms of Pictish family names.)
Where Did The Picts Go
From what I gather, the Picts were absorbed by the Gaelic Scottish people.
What Were the Picts
Historians seem to be unsure if the Picts were Celts or not. Some have argued that the Pictish Language is not part of the group of languages they call Indo-European Languages. And because of that, they are not Celts.
All Indo-European Languages are believed to be descended from a single language often called PIE. And if this is the case, then it suggests that if the Pictish Language is not a descendent of PIE then the Picts may have not been from this group.
Other historians have argued that the Pictish Language is a Celtic Language similar to the Welsh Language, the Gaulish Language, and the Gaelic Language.
It is believed that the Pictish Language was written in Ogham. (This language seemed to be later used for some Gaelic languages -- for the Scottish Language and the Irish Language.)