I believe our American cousins are more familiar for this term to describe those pesky self-sown seedlings and plants that crop up on our plots and gardens in unwanted places. At home its sycamore seedlings that are my bugbear, on my plot it's potatoes. Mind you, last year's volunteer spud crop was my best as they didn't suffer from blight. This year I appear to have a special climbing variety that's managed to find its way into one of my compost bins.
Bet you thought I was going to talk about the other kind of helpful volunteer ;)
For other ABC V posts, hop on over to Mrs Nesbitt's Place.