Definition
A specific airspeed value — 120 knots — expressed as calibrated airspeed, meaning indicated airspeed corrected for instrument and position (installation) error. In the Light-Sport Aircraft context, 120 knots CAS is the maximum level-flight speed at maximum continuous power that an aircraft may have to qualify as a light-sport aircraft (with limited exceptions such as gliders and lighter-than-air aircraft).
Plain English
It's a fixed speed limit — 120 knots — measured in a way that takes out the small errors built into the airspeed indicator and how it's mounted on the aircraft. For an airplane to count as a light-sport aircraft, it can't fly faster than this in level flight at full cruise power.
Context Anchor
Seen in light-sport aircraft eligibility rules and aircraft performance discussions.
Derivation
Calibrated' comes from the Latin calibrare, meaning to measure or adjust to a standard. The airspeed indicator's raw reading (indicated airspeed) is adjusted to a more accurate standard value, giving calibrated airspeed.
Why Pilots Care
This specific speed value defines the maximum allowable level-flight speed for an aircraft to qualify as light-sport under FAA rules.
Grounding Statement
The key point is that 120 knots CAS is a corrected airspeed limit, not just a raw cockpit reading.
Intuition Check
Do not read calibrated airspeed as the same thing as the number shown on the airspeed indicator. CAS is the indicated reading after known errors are corrected; also, knots are not miles per hour.
Example Sentence 1
To meet the light-sport aircraft definition, the airplane's maximum level-flight speed at full cruise power cannot exceed 120 knots calibrated airspeed.
Example Sentence 2
Before certifying the aircraft as light-sport, the builder confirms that V_H stays under 120 knots calibrated airspeed at sea level.