concurrence

Concurrence refers to the state of agreement or to two or more events occurring at the same time. The term derives from Latin con- "together" and currere "to run."

In general use, concurrence is synonymous with consensus or accord, or with co-occurrence when describing events that happen simultaneously.

In geometry, concurrence denotes a property of multiple lines meeting at a single point. Classic examples include the medians, angle bisectors, and altitudes of a triangle, which are concurrent at the centroid, incenter, and orthocenter, respectively. Ceva's theorem gives a condition for three cevians to be concurrent.

In law, concurrence is the requirement that the mental state (mens rea) accompanies the prohibited act (actus reus) for criminal liability; without concurrence, the act may not be punishable.

In computer science, concurrency describes the ability of a system to perform multiple tasks concurrently, often via threads or processes. It contrasts with parallelism, though the two concepts are related. Concurrency introduces issues such as synchronization, race conditions, and deadlock, which require coordination mechanisms like locks and atomic operations.

In quantum information theory, concurrence is a measure of entanglement for two-qubit states. It is zero for unentangled states and increases with entanglement, with a specific mathematical definition involving the state's density matrix.

In statistics and epidemiology, concurrence can refer to the co-occurrence of events or diseases within individuals or populations, used to study comorbidity or joint incidence.