Microsoft Knowledge Base Article 237677 contains the following summary:
The LDAP Data Interchange Format (LDIF) is a draft Internet standard for a file format that may be used for performing batch operations against directories that conform to the LDAP standards. LDIF can be used to export and import data, allowing batch operations such as add, create, and modify to be performed against the Active Directory. A utility program called LDIFDE is included in Windows 2000 to support batch operations based on the LDIF file format standard. This article is designed to help you better understand how the LDIFDE utility can be used to migrate directories.