What is ONB?

ONB most likely refers to Orthonormal Basis. In the context of computer graphics and linear algebra, an orthonormal basis is a set of vectors that are orthogonal (perpendicular) to each other and have a unit length (normalized). Orthonormal bases are fundamental for efficiently representing and manipulating vectors and performing transformations. They are commonly used in areas like shading, lighting calculations, texture mapping, and general 3D geometry processing due to their mathematical properties that simplify computations.