Plain English Meaning
These are the speed caps a pilot has to stay under while flying in a holding pattern. The cap depends on how high you are: slower lower down, faster higher up.
Full Definition
The published upper airspeed limits an aircraft must not exceed while flying a holding pattern in controlled airspace. In the United States, the standard limits are 200 KIAS at or below 6,000 feet MSL, 230 KIAS from 6,001 to 14,000 feet MSL, and 265 KIAS above 14,000 feet MSL. Specific holding patterns may be charted with lower limits, and certain categories of operations (such as USAF and USN airfields, or specific holds in mountainous terrain) use different values.