Definition of substitution. 1  1a : the act, process, or result of substituting one thing for anotherb : replacement of one mathematical entity by another of equal value. 2  2 : one that is substituted for another.
Homogenized milk is any sort of milk that has been mechanically treated to ensure that it has a smooth, even consistency. The homogenization process typically involves high temperatures, agitation, and filtration, all aimed at breaking down milk's naturally occurring fat molecules.
Making the world better, one answer at a time. Milk is a colloid, and is, in fact, heterogeneous because if you look at it under a microscope you can see little globs of fat, but under the naked eye it will look like it is homogeneous.