The number of time periods to delay the start of the task after all other scheduling constraints are met. If something causes the start of a task to be postponed, the Start Delay field can be used to reflect this in the project schedule. For example, if a worker who is indispensable to the completion of a task becomes ill, work on that task may be delayed until the worker returns to work.
Rather than typing a value into this field, you can also delay a task's start graphically in the Gantt view by dragging the task bar to the right the desired amount of delay time. To use this technique, move the mouse pointer slowly over the task bar until the pointer changes to a Delay pointer, then drag the task to the right to increase the delay, or drag to the left to decrease the delay.
By default, in the Gantt chart graphic pane, the delay is represented by a thin, black, dotted line.