Rhubarb-rhubarb Definition

noun

(chiefly UK, film) Background noise of several "conversations," none of which is decipherable since all the actors are actually just repeating the word rhubarb, or other words with similar attributes.

Wiktionary

(chiefly UK, pejorative) Speech which is undecipherable to the listener because it is in a language he or she does not understand; mumbo jumbo.

Wiktionary

(chiefly UK) Blah blah; etc, etc.

Wiktionary

Origin of Rhubarb-rhubarb

Chosen as a word for producing indistinct background noise because it contains no very sharp or recognisable phonemes. Yielded sense 3 of rhubarb.

From Wiktionary