Olla means "pot," and an olla used in the garden is an unglazed pot made from porous clay (usually terracotta) that is buried in the ground and filled with water to irrigate plant roots.Ollas come in different shapes and sizes. The traditional shape looks like a bulbous jug with a long narrow neck. There are others that look more like a wine bottle and some that come as a ball with a piece of irrigation tubing connected to it that then hooks up to a water reservoir system. There are also a variety of DIY versions.