A Hash Message Authentication Code, is a type of message authentication "code" calculated using a specific algorithm that uses a cryptographic hash function in combination with a secret key. It verifies both the data integrity and the authenticity. Any iterative cryptographic hash function, such as MD5 or SHA-1, may be used to calc an HMAC. the resulting MAC is termed HMAC-MD5 or HMAC-SHA1 accordingly.

I surmise they are differentiating between the algo and various hash functions.