Availability is OEE’s first factor: the share of the planned production time in which the equipment is actually running. Availability = running time ÷ planned production time. Losses: breakdowns, changeovers and other stops.
The boundary matters: breaks and planned maintenance can be kept outside planned time, but the definition must be fixed and honest — move losses out of the denominator and OEE rises on paper, while the real capacity is unchanged.
Improving availability goes two ways: fewer stops (preventive maintenance, root-cause analysis on breakdowns) and shorter stops (SMED on changeovers, fast troubleshooting).