This command scans the square directly in front of your cybug. In past versions of the game, we did not have access to this command, and instead had a command called 'scan position ...' (still available in the latest version) where the position was specified absolutely - e.g. position1 was directly north, position 5 was south etc.
Scan Relative 1 is very useful in this game because most cybugs get where they want to go by moving forward (yes I did say 'most cybugs' - there was one very good one a long time ago called Skeeter, by the great Devon Ellis, now of Fleet Commander fame, which moved around backwards for some reason). It's handy to know what's directly in front of you, because if it's a mine or a flag you might want to do something about it.