Complex sentence: Rhyming slang is a form of phrase construction in the English language that is especially prevalent in dialectal English from the East End of London; hence its alternate name, Cockney rhyming slang.
Split into simpler sentences: Rhyming slang is a form of slang word construction in the English language that utilizes rhyme. It is especially prevalent in English from the East End of London; hence its alternate name, Cockney rhyming slang.