The Automatic Terminal Information Service is a radio frequency that broadcasts a looped message to pilots detailing weather, runway conditions, and other vital information. In the olden days, a person in air traffic control would record the ATIS message. Nowadays, the message is generated by a text to speech synthesizer, and automatically updated as conditions change.

Pilots generally listen to their origin airport's ATIS before leaving the gate, and dial in their destination's ATIS before their final approach. Each ATIS recording is given a letter code from the phonetic alphabet, such as "information Alpha." When the pilot contacts clearance delivery or approach control, they tell the controller which recording they have received: that way, everyone is using the same information, and the controller can advise the pilot if anything has changed since the last ATIS recording.

Here is a sample ATIS broadcast, courtesy of

Cleveland Hopkins information India 1755 zulu automated weather wind 260 at 15 gust 19 visibility 6 light snow 2,600 broken 3,500 overcast temperature -5 dewpoint -11 altimeter 2999 ILS runway 23 left approach in use landing runway 23 left departing runway 23 right notice to airmen runway 18 closed readback all runway assignments and hold short instructions use caution for birds in the vicinity of the active runway advise the controller on initial contact you have India
Most aeronautical charts will place ATIS frequencies next to the symbol for the airport, so if you have a Jeppesen chart and a radio scanner, you can listen in.