In addition to a condition, a transition can specify a signal name. When such a signal name is present, the transition is not taken directly, even if the condition evaluates to True. Instead the transition blocks, waiting to be woken up.
In order to wake up a transition with a defined signal name, the signal must be sent to the workflow instance. A common way to send a signal is to use a button in the user interface, using the element button with the signal name as the attribute name of the button. Once the button is clicked, the signal is sent to the workflow instance of the current record. Note-The condition is still evaluated when the signal is sent to the workflow instance.