The word Roger is also used when communicating by
radio, (as in
Roger Wilco, for example). In this
context, 'Roger' means '
message received'.
This use derives from the radio alphabet used by the US Navy in WWII, in which the word Roger was the phonetic representation of the letter R, ('R' as in 'Received').
Nowadays, the accepted phonetic representation of R is Romeo, from the NATO radio alphabet, but once a radio operator gets used to 'rogering', it's a hard habit to break.