From the wikipedia articles on melons:
Melon is a term used for various members of the Cucurbitaceae family with fleshy fruit. Melon can refer to either the plant or the fruit, which is a false berry. Many different cultivars have been produced, particularly of muskmelons. The plant grows as a vine. (Melon - Wikipedia)
Muskmelon (Cucumis melo) is a species of melon that has been developed into many cultivated varieties. These include smooth skinned varietes, such as honeydew, and different netted cultivars known as cantaloupes (Muskmelon - Wikipedia).
Here's a pictorial guide to several melon types:
Cook's Thesaurus: Melons