Final answer:
A slipped milestone on a Gantt chart is commonly represented by a diamond symbol relocated by a dashed line to a new position, indicating a delay.
Step-by-step explanation:
On a Gantt chart, a slipped milestone is typically represented by a symbol such as a diamond that is connected by a dashed line to its rescheduled position. In practice, the original milestone might be shown in a specific color with a line leading to a new symbol, showing that the milestone has not been met as originally planned and has been moved to a future date.
This visual representation helps project managers and team members to quickly see adjustments in project timelines and manage expectations accordingly.