Overview#Directory Information Tree (DIT), refers to the hierarchical structure of the entries in the Directory Information Base. (RFC 4512)
Often RFCs and other documents do not make any distinction and use only Directory Information Tree for both the "Structure" and the "Information"
The Directory Information Tree contains one or more Naming Context, which are the base entries for the server, and every other entry is descended from one of those Naming Contexts entries. That is, a naming context entry is special in that it does not have a parent entry.
The following is a graphical example of a DIT:
In this example, the entry "dc=example,dc=com" is the naming context, and it has two immediate children, with DNs of "ou=People,dc=example,dc=com" and "ou=Groups,dc=example,dc=com", respectively, and each of those entries has its own subordinate entries. There is no predefined limit to the maximum depth of a directory tree, and any entry can potentially have one or more subordinate entries. An entry that does not contain any subordinates is said to be a leaf entry, and any entry that has at least one subordinate entry is called a non-leaf entry.
From RFC 2251
"The LDAP protocol assumes there are one or more servers which jointly provide access to a Directory Information Tree (DIT)."
The largest collection of entries, starting at an entry that is mastered by a particular server, and including all its subordinates and their subordinates, down to the entries which are mastered by different servers, is termed a Naming Context. The root of the DIT is a DSA-specific Entry (DSE) and not part of any naming context: each server has different attribute values in the root DSE. (DSA is an X.500 term for the directory server)."