Hi Erick,
taken from System Reference Guide (
GUI - Operations - Smart RF)
Smart Sensor defines whether a listed Access Point is smart sensor on behalf of the other Access Point radios comprising the RF Domain  Then I assume this refers to Smart-RF operated state which is 
 
- normal - Radio broadcasts  
 - offline - Radio does not broadcast (shut down or fulltime sensor) 
 - sensor - Radio actively measures RF during calibration
 
Regards,
Ondrej