Plain English Meaning
It is the point where a pilot flies across the runway at the middle, at pattern height, and then turns to fly across the wind before joining the normal traffic flow around the airport.
Full Definition
The crosswind leg of the airport traffic pattern when entered from outside the pattern by crossing over the runway at pattern altitude near the middle of the runway, then turning to fly perpendicular to the runway on the upwind side before joining the downwind leg.
Context Anchor
Used when discussing traffic-pattern entries at non-towered airports, especially when a pilot is joining the pattern from the opposite side of the runway.