cryptocurrencies is the umbrella term for all cryptographic based currencies, thus including bitcoin.
then beneath that it separates into bitcoin litecoin and namecoin (the three main first gen) and altcoins, where most the other cheap pump and dump altcoins exist which have atleast 50% code copied from the first gen.
Personally, I would include litecoin and namecoin under the altcoin category, but I recognize that a significant number of people feel that those two stand on their own regardless of how much they are based on Bitcoin and don't consider them to be altcoins.