Until half an hour ago I didn't know that junction points are a particular type of reparse point. A reparse point contains data and a tag which identifies which file system filter is used to process the data. This provides an extension mechanism for NTFS.
Microsoft have provided several type of reparse point from Windows 2000 onwards:
- Symbolic links
- Junction Points
- Volume Mount Points
- Remote Storage Server
This page briefly explains what each of these are.