What does "migration" actually mean?

What does "migration" actually mean?

Migration through the printing substrate
Here, there is a direct migration of ink components through the substrate. The contents would be directly affected. Those ink components which are soluble both in the filling itself and in its components are considered to have a particularly high migration potential. Greasy fillings are notably challenging.

Through setoff migration,

an unwanted contact of the printed and unprinted sides of the packaging can lead to the undesirable transfer of ink components. What is particularly tricky here is the fact that usually the unprinted side is the inside of the packaging and therefore touches the food surface.

Substance transfer through the gas phase

When dealing with separately packaged foods, such as e.g. cereals, gas exchange through the film inner packages can lead to a transfer of undesirable components.