Islandix truing tools use the acronym TIR to describe wheel alignment. Originally TIR stood for Total Indicated Runout but over time became Total Indicator Reading. Technically runout is a measure of concentricity, which applies to radial wheel alignment but not lateral alignment (instead a measure of flatness). Wheelbuilders often say runout when referring to both and that’s fine.
Regardless TIR is a Total measure, that is the maximum reading minus the minimum. On a rim brake wheel, for example, lateral TIR is the difference between shortest and longest spans from rim to brake through a full rotation of the wheel. That’s intrinsically useful.
For various reasons some wheelbuilders prefer to describe alignment in plus-minus terms. In this nomenclature alignment is given as the difference between minimum/maximum readings and the midpoint. If you prefer thinking about alignment in plus-minus terms, divide TIR by two.