Yak is to talk, and to talk, and to talk some more.
It is to talk endlessly and tirelessly.
And majority of the times, yakking is all about senseless babble and chatter.
Do remember Yak is a wild, shaggy-haired ox as well. Look up its images on Google.
Yak carries the following dictionary definitions:
1. To talk, especially uninterruptedly and idly; gab; chatter
Usage examples for yak:
1. They’ve been yakking on the phone for over an hour.
2. Women are in the habit of yakking: they can just go on and on about matters.