What is homogenized milk?

The fat globules are mechanically reduced in size so they don't rise up to the top of milk

In regular milk, the cream rises to the top. The reason being that the fat globules are too large and float to top. Homogenization is a mechanical process where the milk is passed through very small holes to reduce the size of fat globules. These smaller fat globules just remain suspended and don't rise to top. In the olden days when someone bought a bottle of milk, you could see the cream at top. People thought it was very un-seeming so the homogenization process became a marketing tool. You did not have to shake the bottles to mix the cream. It also was in the economical interest of dairy industry so they could make other products from the cream such as butter.