Glossary
RunLevel
The Principal element that decides whether a scheduled task runs with the account's least privileges or with its highest available (administrator) token.
RunLevel accepts LeastPrivilege (the default) or HighestAvailable (Task Scheduler schema). For an administrator account, HighestAvailable means the task runs with the full, elevated token, the equivalent of "Run with highest privileges" in the console. For SYSTEM it makes little practical difference, since SYSTEM is already fully privileged.
A non-Microsoft task with HighestAvailable or a SYSTEM principal is a triage priority, though many security and backup agents are configured this way. See detecting malicious scheduled tasks.