Reliability engineers are interested in the probability that equipment or a component
of that equipment will survive a certain time, meaning there is no failure in that
stated time. If you take the above definition of the cumulative distribution function
F(x) it can be said the reliability function or survival function must be the complement.
If F(x) is the chance it will fail, then reliability can be defined as 
You may also conclude that F(x) is unreliability.