Orthogonality

The term derives from geometry, where two lines are orthogonal when they meet at a right angle — their directions are entirely independent. In mathematics and physics, the metaphor extended to vectors and functions that share no mutual influence. Andy Hunt and Dave Thomas brought it explicitly into software design in their 1999 book The Pragmatic Programmer, using it to describe systems where changing one component leaves all others unaffected — and establishing independence as a measurable quality of good architecture.