Rel may mean:
- Rel, the category of sets and relations
- Rights Expression Language, a machine-processable language used for Digital Rights Management
- Rel (DBMS), a database management system
- rel, an HTML attribute for indicating a semantic link
- REL, a file format generated by Microsoft's M80 and Digital Research's RMAC for CP/M
- Recommended Exposure Limit, a recommended limit for occupational exposures published by the National Institute for Occupational Safety and Health
- Rel proteins, A family of related proteins (includes NF-κB family members).
- Rel, A Dalek unit of time measurement roughly equal to one second.