Nines
Noun · Slang · Slang & Abbreviations
Definitions
Shorthand for uptime percentages. 'Three nines' = 99.9%, 'five nines' = 99.999%. Each additional nine is exponentially harder and more expensive to achieve. The difference between three nines and five nines is the difference between 8.7 hours of downtime per year and 5.3 minutes.
In plain English: A way to express how reliable a service is — 'five nines' means 99.999% uptime, or less than 6 minutes of downtime per year.