All anomalous objects, entities, and phenomena requiring Special Containment Procedures are assigned an Object Class. An Object Class is a part of standard SCP template and serves as a rough indicator for how difficult an object is to contain. 

In universe, Object classes are for the purpose of identifying containment needs, research priority, budgeting, and other considerations. An SCP's Object Class is determined by a number of factors, but the most inportant factors are the difficulty and the purpose of its containment.

 SAFE  Anomalies in this class are easily and reliably contained.

 EUCLID  These anomalies require more resources for containment or where containment is not always reliable.

 KETER  These are the most difficult to contain, requiring extensive and complex procedures.

 THAUMIEL  Used by the Foundation to contain other SCPs.

 NEUTRALIZED  The SCP no longer poses any threat.

 EXPLAINED  An SCP that can now be fully explained by science. 

 APOLLYON   Uncontainable and will lead to the end of the world. (Apocalyptic)

 ARCHON  Containable, but deliberately left uncontained for practical or moral reasons.

 DECOMMISSIONED  An SCP removed from the database, usually for narrative or meta reasons.

 CERNUNNOS   An anomaly created by the Foundation itself.

 TICONDEROGA   An anomaly that is either memetically resistant to understanding, or completely incomprehensible.