Backslang is an unusual form of slang in which words are reversed phonemically (i.e. by sound), in order to make it harder for people to understand what the speakers are saying. There is a theory that backslang originated between market sellers in Victorian England, who wanted to have private conversations with their assistants or fellow sellers in order to trick customers into paying more money for poorer quality goods. In this way, backslang is fairly similar to Cockney rhyming slang which was purportedly invented so criminals could discuss illicit matters while evading the attention of the police.
The word “yob” – meaning a loutish or uncultured young male – though primarily used in British English, is an example of backslang (“boy” reversed). Most backslang, however, hasn’t entered standard English. A few more examples of backslang are words like “dello” (“old”), “erif” (“fire”), “elsop” (“police”) and “retchtub” (“butcher”).
Backslang is also apparently used in prisons in order to hide their conversations from guards.