A type of nymph, dryads are the spirits of trees. Though the Greek word drys signifies oak trees specifically, the term 'dryad' has since come to refer to all tree nymphs regardless of tree type. They are said to be very shy around everyone, save for Artemis. Some other types of dryads are the Meliai (ash trees), Epimeliads (apple trees), and Caryatids (walnut trees). The Meliai in particular played a large role the life of Zeus, as they were appointed by his mother, Rhea, to tend to him when he was an infant.
Like all nymphs, dryads are potentially immortal and their lives are tied to their homes. Some dryads, called hamadryads, are even part of their trees to the point that, if the tree dies, they die with it.
In Young Hercules
"1.20 - Fame" - When Cheiron tells Hercules that 'the undead can only be defeated by their own'. Thus, to defeat Bacchus for good, he and Iolaus go to the desert to collect dryad bones. These dryads, rather than being inhumanly beautiful tree spirits, are large, humanoid skeletal monsters with bat-like wings and a long tail. They can burrow through the sand, identical to Sand Sharks. Springing out of the sand, they are animated enough to hover in the air without anything visibly holding the skeleton together. They are easily beaten in a fight, though, thankfully.