Posterior comes from the Latin word posterus, meaning coming after. Posterior is often used as a technical term in biology and medicine to refer to the back side of things, and is the opposite of anterior, which refers to the front side. For example, as more people took up running as a sport, doctors began to see an increase in stress fractures along the posterior as well as the anterior surface of the lower leg bones. In some technical fields, posterior may mean later. When used as a noun, posterior simply means buttocks. Origin and Etymology of posterior Latin, comparative of posterus coming after, from post after â more at post-