You are thinking of the consumer Call Waiting service. The relevant vocabulary here is the extensive, industry-standard terminology of ACD (automatic call distribution) systems. "Hold" can occur only after a call has been answered by an operator:
"Average Hold Time (HDCP time)
The average amounts of time per Answered ACD call that an agent (or agents) placed an ACD call on hold. Handling time is measured from the time the agent puts the ACD call on Hold to the time the agent becomes active on the call again or the caller abandons the call. The average Hold time is the sum of all ACD call hold times divided by the number of ACD calls answered by the agent or ACD queue. When the telephone system data includes Hold time, the average Direct Call Processing time does not include the Hold time. In this situation, the Average DCP time is the time that the agents are active on the call, excluding holding time of ACD calls."
Hold time is part of *call duration*. The time in queue until the call in answered by an operator is *wait duration* or "call waiting time".
See, for example,
http://whatis.techtarget.com/definition/0,,sid9_gci1188654,0...or
http://queuemetrics.com/manuals/QM_U