What exacly means positon and hold?
From the Pilot/Controller Glossary:
POSITION AND HOLD- Used by ATC to inform a pilot to taxi onto the departure runway in takeoff position and hold. It is not authorization for takeoff. It is used when takeoff clearance cannot immediately be issued because of traffic or other reasons.
It's mainly used to taxi departure traffic onto the runway and clear him/her for takeoff once landing or other traffic occupying the runway has cleared the runway.
It eliminates delays since the aircraft is already on the runway, they just need takeoff clearance.
Hope this helps,