This word kept popping up in a mobile game I play, so eventually I gave it a Google. I assumed damson must be an insect of some kind...but it's...a kind of plum!
Chiefly found in Europe, the damson used to be known as a damascene. Legend has it that the plums were introduced to Great Britain by Romans, although this link has not been firmly proven.
By Jonathan Billinger, CC BY-SA 2.0, Link