Availability is the percentage of time an asset is able to perform its function.
Availability is the number operations actually cares about: was the asset there when we needed it? Enter your period and downtime to get operational availability, then split the downtime to see how much you're losing to repairs versus waiting. The gap is usually the real story.
The share of scheduled time an asset is up and able to run, rather than down for repair or maintenance.
Uptime divided by total scheduled time. For inherent availability, divide MTBF by the sum of MTBF and MTTR.
Reliability is how long an asset runs before it fails. Availability also reflects how fast you restore it after a failure.
It varies by industry and criticality. Continuous process plants often target the high 90s for critical assets.