What does Modified mean ?
“Modified ” is defined for a task as the latest time at which the task got updated
Here are specific instances when the 'Modified' time for a task will be updated:
Task creation.
Change in assignee for the task.
Task acceptance.
Updates or additions to global and form attributes.
Core attributes [priority, description, scheduling, work order number e.t.c ]
Change in task status.
Update of estimated time.
Linked task added or removed
Watcher updates