1) The use of a rhyming word in the place of the original word to obscure the meaning.
2)The chaotic blur that is the soul of the Cockney dialect.
"Take a butcher's" (butcher's hook = look)
Daisies (shoes) (daisy roots = boots).
"She's a pretty twist" (twist and twirl = girl)
"He's ginger" (ginger beer = queer / homosexual. Derogatory unless uttered by fellow travellers)
"I took the lift to the apples"(apples and pears = upstairs, though not even pensioners use that phrase anymore)
Generally rhyming slang is a load of old bollocks. In the words of terry pratchett "it is made up to annoy strangers, which is the case with most slangs"
Whoa rhyming slang makes no sense!
prunes (syrup of)=wig
apples and pears=stairs
busy bee=general theory of relativity