Freegan can be seen as a special way of vegetarianism. Freegans eat milk and egg products (some of them even eat meat) if it's not been bought or otherwise organized in a way that supports market practices.
A typical way of living freegan is so-called dumpster diving. That means people take foods out of the dumpsters of supermarkets. Supermarkets often throw away products which are still edible and healthful. The reason is that if a product's date of expiry has passed by only a few days, food products usually go into the dumpster (as they are required to be by the health department). So a lot of still very good stuff can be found.
There are even dumpster divers that only use organic food shops for their tours.
The idea of freeganism is that one does not want to support the production of milk, eggs and meat, but has no problem in consuming them. If the products are taken out of dumpsters, they don't play any role in the market, no money or other motivations are created to produce more animal food.