In a nutshell, a "milk jug" is a term used in some parts of the world to describe a "creamer" - the vessel included in most tea sets which is intended to hold milk or cream for use in coffee and tea. This phrase could also refer to a larger pitcher used for holding milk.
A milk jug cover can be fancy or plain, but it's basically a topper for the milk jug. When crocheted, milk jug covers typically resemble doilies. They often include beads, buttons or other baubles around the edges which add extra weight.
Milk jug covers were popular in Australia. Some crocheters still enjoy making them, and many collectors enjoy locating vintage examples for their collections.
More Information About Milk Jug Covers:
The following articles feature interesting historical and cultural information about milk jug covers and their evolution.