Finish No Earlier Than (FNET) is a start/finish constraint that schedules a task to complete after the date you specify. If this field is selected, then a date must be input in the planned completion date field.
This constraint option is typically used when the project's schedule mode is set to Schedule From Complete Date. When this is the case, it allows a project manager to provide a soft constraint on the task before it forces other dependent tasks to show as At Risk.
If FNET is used on a Schedule From Start Date project, then the constraint will schedule the task as it would an As Soon As Possible task.