Traditional meads are usually made with just honey and water, the different flavors come from the types of honey, yeasts, and/or aging process employed.
Melomel is a catch all for mead made with fruit that does not fit another category.
Metheglin is mead with herbs or spices added. Some examples might be ginger, nutmeg, coriander, cinnamon, and/or vanilla.
Cyser is type of melomel made with apple juice, usually in place of or addition to the water normally used.
Pyment is a type of melomel made with grape juice.