Glossary
LogonType S4U
A scheduled task principal setting that runs the task as a user without storing the password, with no access to network resources by that user's credentials.
LogonType in a task's Principal element accepts InteractiveToken, Password, S4U and the legacy InteractiveTokenOrPassword (Task Scheduler schema). S4U (Service for User) lets the task run whether or not the user is logged on, without a stored password; the resulting token cannot use the user's credentials on the network.
Password is different: the credentials are stored so the task can run while the user is away, and Microsoft recommends alerting on it in event 4698. See detecting malicious scheduled tasks.