Plain English Meaning
A standard briefing is the full weather and flight information package a pilot requests before a flight when they haven't yet gathered any weather details. It covers everything they need in one go, in a set order.
Full Definition
A standard briefing is the most complete type of preflight weather briefing provided by Flight Service, given when a pilot has not received any prior weather information for the planned flight or when an updated complete picture is needed. It includes adverse conditions, a VFR flight not recommended statement (when applicable), synopsis, current conditions, en route forecast, destination forecast, winds aloft, NOTAMs, and ATC delays, in that established order.