Definition
Metal loops or eyelets attached to the underside of an airplane's wings and tail (and sometimes the fuselage) that serve as anchor points for ropes, chains, or straps used to secure the aircraft to the ground when parked.
Plain English
Small metal rings built into the airplane that you tie ropes to so the wind cannot move or flip the airplane while it is parked.
Context Anchor
You encounter tie down rings during post-flight securing, especially when parking an airplane outside on a ramp or tiedown area.
Why Pilots Care
Proper use prevents wind from lifting or shifting the aircraft, avoiding airframe damage and costly repairs.
Analogy
Like the rings on a tent that you stake into the ground so the whole shelter stays put in strong wind.
Intuition Check
Do not think of these as decorative rings or loose hardware. In this context, tie down rings are load-holding attachment points used to secure a parked aircraft.
Example Sentence 1
After shutdown, she attached ropes to the tie down rings under each wing and the tail before walking away from the airplane.
Example Sentence 2
Before a storm arrived, the instructor double-checked that all tie down rings were fastened with chains.