Posterior

Posterior is a term used to denote the back or rear relative position in anatomy and a concept in statistics. Etymology: from Latin posterus meaning coming after or behind.

In human anatomy, posterior is a standard directional term opposite anterior. It is applied to surfaces, walls, and regions to describe relative location, such as the posterior aspect of the head, the posterior chamber of the eye, or the posterior compartment of the leg. In anatomical descriptions, posterior generally means toward the back when the body is in the standard anatomical position (standing, arms at the sides, palms facing forward). In animals without upright posture, posterior corresponds to toward the tail. The term is widely used in clinical discussions, imaging, and surgical planning to specify where a structure lies.

In statistics, posterior refers to the posterior distribution or posterior probability in Bayesian inference. The posterior distribution represents updated belief about a parameter after observing data, combining a prior distribution with the likelihood of the data via Bayes' rule: P(θ|x) ∝ P(x|θ)P(θ). Common tasks include computing posterior means or medians, credible intervals, and posterior predictive distributions for future observations.

Related terms include anterior (front), and, in other contexts, dorsal/ventral or superior/inferior. The word is used across disciplines to denote what comes after or behind, whether in physical orientation or in probabilistic reasoning.