Poaching is a delicate and subtle way of cooking. You poach things below boiling point in just enough liquid to cover them, and that can be water, court bouillon (a flavoured stock made with wine, peppercorns and a wrap of herbs), stock or milk. Generally you use first-class cuts of meat and fish which need gentle cooking — you’ll be surprised at the results of poaching a fillet steak, for example. It will taste really tender and clean.
Boiling is a great method of cooking. It involves cooking stuff in a liquid at its boiling point. You can use water, court bouillon, milk or plain stock. Boiling liquid is a direct source of heat, so vegetables can be very quickly cooked, but be careful not to over-boil like my nan does or you’ll end up with green water and grey greens! When boiling meat you’re generally using tougher cuts, which will need to have their tough sinews melted away. In return you will get tender meat and a tasty stock.