One of the most frequent questions asked by newly designated LDAP administrators is, "What do all of these abbreviations mean?" Of course, the question refers to things such as cn, c, and sn. There is no single source of information describing all possible LDAPv3 attribute types and object classes, but there are a handful of online sites that can be consulted to cover the most common schema items:
The documents outlined in RFC 3377 provide a list of references for researching related LDAPv3 and X.500 topics. RFC 2256 in particular describes a set of X.500 schema items used with LDAPv3 directory servers.
This site, maintained by Alan Knowles, provides a nice means of browsing descriptions and dependencies among common LDAP attributes, object classes, and OIDs.
This site can be helpful in tracking down the owner of specific OID arcs.
The SunOne Directory Server, formerly owned by Netscape Communications, includes a large set of reference documentation on various LDAP schema items. Even if you are not using the SunOne DS product, the schema reference can be helpful in understanding the meaning of various LDAP acronyms. Search the site for "LDAP schema reference" to locate the most recent versions of the product documentation.