Plain English Meaning
The pilot is saying, 'Yes, my aircraft and I are ready and legal to fly on instruments right now.' It's a confirmation that everything needed for IFR flight is in place.
Full Definition
A statement by the pilot that the aircraft is properly equipped, the pilot is appropriately rated and current, and the flight can be conducted under Instrument Flight Rules. Used by ATC to confirm a pilot's ability to accept an IFR clearance, particularly when weather, terrain, or traffic make VFR flight impractical.
Context Anchor
Used when air traffic control or FAA guidance is discussing whether a pilot can accept radar assistance, a , or a that requires instrument flight rules.