Secure. Contain. Protect.

Special Containment Procedures
It is the motto of The SCP Foundation, which keeps supernatural entities or objects from affecting normal human life.
The classes -
Safe: Can be contained easily.

Euclid: Abnormal entities or objects that can be contained easily following specific orders.
Keter: Requires extremely specific containment procedures, and are difficult to contain effectively.
Thaumiel: Are capable of and in some cases actually used by the Foundation to contain and/or counter-act other SCPs, usually Keter ones.