SpO2 (oxygen saturation)
Shows what percentage of the oxygen carriers in your blood are full. It is measured with a small clip worn on the finger.
A little more detail
An estimate of arterial haemoglobin oxygen saturation measured by pulse oximetry from light absorption. In healthy people at sea level it is usually 95% or higher; device accuracy falls at low saturation, with movement and with poor circulation.
Source: Jubran A. Pulse oximetry. Crit Care. 2015;19:272. doi:10.1186/s13054-015-0984-8