|Definition:|| in a set where a multiplication is defined, unique element u, if it exists, such that for any element a|
Note 1 to entry: For numbers, the neutral element for multiplication is the number one, denoted by 1. For square matrices, it is the unit matrix of the same order. For quantities, the neutral element is a quantity of dimension one (or dimensionless quantity) whose numerical value is the number one. For dimensions of quantities, the neutral element is the dimension of the quantities of dimension one, denoted by the symbol 1.