Linear mass density or simply linear density is defined in the International System of Quantities (ISQ) as the quotient of mass and length. It is also called titer in textile engineering.
Although (linear) density is most often used to mean (linear) mass density, the concept can be generalized for the any other quantity per unit of length, called lineic quantities in ISQ.For example, linear charge density or lineic electric charge is the amount of electric charge per unit length.