When an incident includes a breach of physical security, all aspects of physical security should be escalated under a containment strategy known as

When an incident includes a breach of physical security, all aspects of physical security should be escalated under a containment strategy known as a lockdown. 

During a lockdown, everything and everyone is held until the issue is taken care of. A breach of security can happen when someone tries to hack into a system and steal information. By having a lockdown, it allows the organization to try and get the issue situated before possibly having more information leaked.