"Volunteers," in the gardening world, are plants that volunteer coming up and growing without your assistance of planting the seed or seedling. They usually are reseeded from nearby plants of the previous year. Sunflowers, and some of the easy-to-reseed herbs like Lamb's Ears, garlic chives, and dill happily volunteer just about anywhere and make me crazy each season pulling and ditching them. Cherry tomatoes also enjoy volunteering at the oddest of spots. It's been probably 15 years since I bought and planted Sweet Annie (artemesia annua), a fragrant herb used in wreath making, but also a host plant for beneficial insects like ladybugs. Some folks use the herb medicinally. I'm still finding volunteers growing in the strangest of places. The plant in the pic was dug up in the rhubarb patch. Sweet Annie doesn't get ditched... it was replanted in the herb garden so the ladys have a home for the summer.