What does "palisade" mean?

Palisade: Any fence made of pales or sharp stakes. Palisade cells (Bot.), vertically elongated parenchyma cells, such as are seen beneath the epidermis of the upper surface of many leaves. -- Palisade worm (Zoöl.), a nematoid worm (Strongylus armatus), parasitic in the blood vessels of the horse, in which it produces aneurisms, often fatal.