Plain English Meaning
When the airplane gets into an unusual attitude, the screen automatically hides extra clutter so the pilot only sees what is needed to recover.
Full Definition
On a glass cockpit Primary Flight Display, decluttered information refers to non-essential symbology and data that is automatically removed from the screen when the system detects an unusual attitude, leaving only the attitude indicator, airspeed, altitude, and other recovery-critical references visible.
Context Anchor
Seen in discussions of modern flight displays, especially during high-workload situations such as unusual attitude recovery.