Amount of change in a linear dimension per unit temperature change. Uses units of strain (unitless ratio of length change to original length) per unit temperature (temperature change). Positive temperature change is assumed (i.e. heating up).
Also called the coefficient of linear thermal expansion. A related, but seldom used, property is the volumetric thermal expansion, which, for isotropic materials, is equal to three times the linear.
Dimensionally-sensitive mechanisms need to account for dimensional changes brought on by changes in temperature. This is particularly vital if two parts with significantly different thermal expansion values are mated rigidly.
ASTM testing standards include D696, E228, and E831. ISO standards include 4897, 11359-2, and 17744.