Explanation of openssl ciphersuites
What is ADH? Where is it standardized?


ADH stands for Anonymous Diffie-Hellman, ie unauthenticated Diffie-Hellman, also called "opportunistic encryption". It has been part of the SSL/TLS standards at least since SSLv3. It was also extended to ECDHE in RFC4492.


  The listed MAC algorithms are hash functions. Is it using HMAC?


Yes indeed.


  What does "Au" mean?


It most likely means something like Authentication mechanism. This clearly covers with the given ciphersuites as ADH suites have none there, RSA key-transport and DHE+RSA suites have RSA there (server authenticated via RSA signature), DHE+DSS suites have DSS there (server authenticated via DSA) and suites using static DH ones have DH there (server authenticated via his static DH public key).