What does system resiliency refer to, and how do you achieve this?

"A system is considered resilient if it can continue to function even though other parts of the IT infrastructure have failed or are no longer available. This is especially important in mission-critical systems, which perform functions important to the operations of the organization. Some of the methodologies I use to ensure system resiliency include redundancy, backups, isolation, delegation, and containment. Reducing the impact of any system failure and preventing it from spreading to other systems is key to maintaining high availability and keeping the organization's business processes functioning."