Honey is a new method of catching pokemon introduced in Pokemon Diamond and Pearl. When put on certain trees, you have to check the tree later. Sometimes there is a pokemon. You can tell what trees to put honey on by their yellow coloration. You can buy honey from a salesman in the Floarama Town Meadow, located north of Floarama Town. Each honey costs 100 poke dollars. You can find honey throughout the game as well. The pokemon Combees' ability will find honey as you travel with it in your active party. In Floaroma Meadow, there is a lot of hidden Honey.
Pokemon found by using honey
Silcoon (Pokemon Diamond)
Cascoon (Pokemon Pearl)