With Call Hold, the subscriber can hold the existing connection and switch to the new connection. Afterwards he can switch back to the original connection. If the user switches back and forth between the two connections, then he is toggling.
The hold state is signaled by the hold tone. This signals the voice interruption to the other party, while the subscriber can make a consultation call to a second party. Call hold is described in ITU-T Recommendations I.253 and Q.733.2.