Hello and welcome to Just answer,
Bank 1 is the rear bank of cylinders (next to bulkhead) Bank 2 is front bank of cylinders (next to radiator)
Sensor 1 is the HO2S in the Exhaust manifolds before the convertors Sensor 2 is the HO2S after the convertors.
Bank 1 Sensor 2 is the sensor after the convertor for the pipe leading to the rear bank of cylinders.
An o2 sensor code can be set for other reasons other than the sensor itself,
The O2s just report a condition that is outside of the norm. It is up to the technician to run the diagnostic chart for the code set to determine if a condition is actually present (sensor reporting correctly) or the sensor is NOT reporting correctly because of a faulty sensor.
The PCM looks at both sensor 1 and 2 to monitor the convertors operation, it is possible that the convertor could be faulty or some other reason depending on the exact code set in the PCM each O2 sensor has about 11 codes it could set.