A language that can be used to communicate in a group without everyone there understanding you. A way to talk to about people around you and they won't understand.
You take the first letter of a word and put it in the end, then add 'ay' on the end. It's hard at first but the more you do it the easier it becomes to understand.
English -'Dude, check out that girl, she'd get it so hard'
Backslang -'Udeday, heckcay utoay hattay irlgay, he'dsay etgay tiay osay ardhay'
English -'Hello there, how are you?'
Backslang -'Ellohay heretay, owhay reaay ouyay?'