Plain English Meaning
It's how long you fly on the part of a holding pattern that points back toward the fix. You aim for one minute below 14,000 feet, or one and a half minutes above. You change the length of the other side of the pattern to make the inbound side come out right.
Full Definition
In a holding pattern, the elapsed time flown on the inbound leg toward the holding fix. At or below 14,000 feet MSL, the inbound leg is timed to be one minute; above 14,000 feet MSL, it is timed to be one and a half minutes. The outbound leg is then adjusted on subsequent circuits so that the inbound leg matches this target time, compensating for wind.
Context Anchor
Used in instrument holding procedures when setting or adjusting timing for each trip around the .