Plain English Meaning
When you're flying a holding pattern, you fly one direction toward the fix and the opposite direction away from it. Outbound timing is how long you fly the away-from-the-fix leg before turning back. The standard is one minute lower down, and a minute and a half higher up.
Full Definition
In a holding pattern, the timed leg flown away from the holding fix on a heading parallel to the inbound course. At or below 14,000 feet MSL, outbound timing is one minute; above 14,000 feet MSL, it is one and one-half minutes. Timing begins abeam the fix, or wings-level on the outbound heading if the abeam position cannot be determined.
Context Anchor
Used during instrument holding, especially when correcting for wind to make the inbound leg come to the required time.