A dryad (Δρυάδες, sing.: Δρυάς) is a tree nymph, that is a female spirit of a tree, in Greek mythology. In Greek drys signifies "oak". Thus dryads are specifically the nymphs of oak trees, though the term has come to be used for all tree nymphs in general. "Such deities are very much overshadowed by the divine figures defined through poetry and cult," Walter Burkert remarked of Greek nature deities. They were normally considered to be very shy creatures, except around the goddess Artemis, who was known to be a friend to most nymphs.