What is “availability” and "reliability" mean regarding turbines? How does the system determine the performance of the power plant based on these values?

Reliability: Probability of not being forced out
of service when the unit is needed – includes
forced outage hours (FOH) while in service,
while on reserve shutdown and while attempt-ing to start normalized by period hours (PH)-
units are %:
Reliability = (1-FOH/PH) (100)
FOH = total forced outage hours
PH = period hours
Availability: Probability of being available,
independent of whether the unit is neededincludes
all unavailable hours (UH) – normalized
by period hours (PH) – units are %:
Availability = (1-UH/PH) (100)
UH = total unavailable hours (forced outage,
failure to start, scheduled maintenance
hours, unscheduled maintenance
hours)
PH = period hours

Availability: Probability of being available,
independent of whether the unit is neededincludes
all unavailable hours (UH) – normalized
by period hours (PH) – units are %:
Availability = (1-UH/PH) (100)
UH = total unavailable hours (forced outage,
failure to start, scheduled maintenance
hours, unscheduled maintenance
hours)
PH = period hours

Reliability is the machine availability including planned outage hours only,

Availability includes both forced / planned outages