Rhyming slang is a form of slang word construction in the English language. It is especially prevalent among Cockneys in England. The construction of rhyming slang involves replacing a common word with a phrase of two or more words, the last of which rhymes with the original word; then, in almost all cases, omitting, from the end of the phrase, the secondary rhyming word. The form of Cockney slang is made clear in the following example. The rhyming phrase "apples and pears" is used to mean "stairs". Following the pattern of omission, "and pears" is dropped, thus the spoken phrase "I'm going up the apples" means "I'm going up the stairs".

Source: Wikipedia