An indication that something spoken or written is predictable, repetitive or tedious.
This phrase is a modern-day equivalent of ‘blah, blah, blah’ (which is early 20th century). It is American an emerged during or just after the Second World War. It was preceded by various alternative forms – ‘yatata, yatata’, ‘yaddega, yaddega’ etc. The earliest of these that I have found is from an advertisement in an August 1948 edition of the Long Beach Independent:
“Yatata… yatata… the talk is all about Chatterbox, Knox’s own little Tomboy Cap with the young, young come-on look!”
All of those versions, and including ‘yada yada’, probably took the lead from existing words meaning incessent talk – yatter, jabber, chatter.
‘Yada yada’ itself is first found in the 1980s, in The Washington Post, January 1981:
“I’m talking country codes, asbestos firewalls, yada yada yada.
Lenny Bruce used something very like it in the 1960s though in his Essential Lenny Bruce, 1967:
“They’re no good, the lot of them – ‘Yaddeyahdah’ They’re animals!”
In the 21st century the place you are most likely to come across it is when installing software. For example, the millions who have installed the Google Toolbar will have seen (although probably not read any further than) the instructions – “Please read this carefully – It’s not just the usual yada yada.”