Pronounced "yock", it combines the wordsYACK and TALK, and refers to the act of just babbling endlessly without much meaningful/legitimate content.
Radio listener, irritably switching off a live interview of a politician bragging about all the supposed "progress" he's made in his still-squalid jurisdiction: Okay --- enough of that BS... got better things to do than listen to HIS yalk for the next two hours!
A person pretending to be something they aren't, or an impostor. This is inferred because of the old alien movies where alien pods appear on earth and the "pod people" dispose of the humans and slowly reproduce the bodies, pretending to be humans.
The pod person was pretending to be my father, but I knew that he was an alien when he acted differently than my father ever would have.