What does "Information " in ATC transmissions mean?
This is a simple versioning system used in ATIS (Automatic Terminal Information Service).
ATIS messages contain information about the weather at the airport, runways in use etc. This information is transmitted on a dedicated radio frequency and repeated in a loop. The ATIS messages are updated frequently as the weather or operations at the airport change. Every time a new ATIS message is generated, the letter is changed. 

Example of an ATIS message:


  This is Schiphol arrival information Kilo, main landing runway
  18Right. Transition level 50. Two zero zero degrees, one one knots.
  Visibility 10 kilometres. Few 1300 feet, scattered 1800 feet, broken
  2000 feet. Temperature 15, dewpoint 13. QNH 995 hectopascal. No
  significant change. Contact Approach and Arrival callsign only. End of
  information Kilo.


Now when for example the temperature or pressure at the airport changes, the ATIS information is updated: 


  This is Schiphol arrival information Lima, main landing runway
  18Right. Transition level 50. Two zero zero degrees, one two knots.
  Visibility 10 kilometres. Few 1300 feet, scattered 1800 feet, broken
  2000 feet. Temperature 16, dewpoint 13. QNH 994 hectopascal. No
  significant change. Contact Approach and Arrival callsign only. End of
  information Lima.


The flight crew will listen to the ATIS often before they are in contact with the Air Traffic Control of the airport. They note the information in the ATIS, together with the information version letter. 

On first contact with the airport's Air Traffic Control they will state what version of the ATIS they have listened to. 


  Schiphol approach, this is KLM1234 with information Lima.


The Air Traffic Controller can then determine whether this is the latest version of the ATIS or if there is newer information available that should be passed on to the flight crew.