Start No Later Than (SNLT) is a start/finish constraint that schedules a task to start prior to the date you specify.
If you select this value, then you must input a date in the Planned Start 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 a task before it forces other dependent tasks to show as At Risk.
If SNLT 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.