RR

• low or medium frequency radio range stations

  General

• radar range station

  General

• report immediately upon reaching

  ATC

• report reaching

  ICAO

RR has 4 meanings; the right one depends on context. A weather report, a NOTAM or an ATC clearance. Got a NOTAM full of contractions? Paste it into the decoder.

Source: FAA Order JO 7340.2 Contractions. Not for operational use.