English: high availability 
Welsh: argaeledd dibynadwy 
Subject: TGCh
Welsh definition: In information technology, high availability refers to a system or component that is continuously operational for a desirably long length of time. Availability can be measured relative to "100% operational" or "never failing." A widely-held but difficult-to-achieve standard of availability for a system or product is known as "five 9s" (99.999 percent) availability