"Jumping the quorum" refers to one sub-quorum group of a governing body discussing public business and then telling another sub-quorum group of the body what's going on, so you have, in effect, a quorum of the body discussing things--just in two or more steps.
That appears to be what the Yakima City Council is doing according to this story in the Yakima Herald-Republic.
This came to light because the newspaper obtained city council members' emails through the Public Records Act.
NOTE: The story quotes Greg Overstreet of Allied Law Group. Also note that Allied Law Group represents the Yakima Herald-Republic.