KST ("known or suspected terrorist") is a law‑enforcement/intelligence category for people "known to be or appropriately suspected" of involvement in terrorism. "Known" usually means arrested/charged/convicted for terrorism or formally identified as a terrorist or member of a terrorist organization; "suspected" means there is reasonable suspicion of participation in, preparation for, or support of terrorism. Individuals are placed through interagency nomination to the Terrorist Screening Center’s Terrorist Screening Database (TSDB); only authorized government agencies can nominate, supporting documentation must be on file, and internal and external legal/privacy oversight reviews watchlisting practices.