Directional

Directional is an adjective meaning related to direction or indicating a route or orientation. In general use it describes something with a preferred or specified orientation, especially where movement, measurement, or perception depends on the direction being considered.

In mathematics and physics, directional concepts include the directional derivative, which measures how a function changes as one moves in a particular direction. A direction is often represented by a unit vector, and the rate of change in that direction is given by the dot product of the gradient with the direction vector. Directional vectors and gradients describe how quantities vary with orientation in space.

In biology, directional selection is a mode of natural selection in which one extreme phenotype is favored over others, shifting the population mean in that direction over time. It contrasts with stabilizing selection, which favors intermediate phenotypes, and disruptive selection, which favors extremes.

In engineering and technology, devices described as directional are optimized to manage or channel energy, sound, or signals toward specific directions. Examples include directional antennas for communications, which concentrate radio waves in particular directions, and directional microphones, which are more sensitive to sound from a chosen angle while suppressing others.

In navigation and everyday use, directional terms like north, south, or left and right guide movement. Directional indicators, signs, and compasses help determine orientation and route choice. In software and systems, directional behavior may describe outputs that depend on orientation or input direction.