A320
Flight Crew Total 11508; Flight Crew Type 10520
Distraction; Workload
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Airport; Human Factors; Procedure
We were taxiing single engine on taxiway Q to runway 8R for departure behind another Airbus.  We received our final weights at the gate and I made a quick comment back at the gate that we had them and placed them on my tray table next to the checklist.  Ground told (the other Airbus) they were following a 737 which was on taxiway N or M abeam taxiway Z and to switch to Tower.  I looked ahead and at first did not see many aircraft down by the runway and suggested starting the second engine.  The Captain counted about 6 or 7 airplanes down there and said we can hold off.  While passing taxiway Y ground told us our sequence is the Airbus in front of us and to switch to Tower.  As we approached Paxiway P; I asked about starting the second engine as I saw three or four aircraft on taxiway M or N; one of which was the 737; and just the Airbus in front of us.  The captain said we can hold off.  We stopped on Q near taxiway Z behind the Airbus.  After a RJ deprted 8R but before the 737 did; tower cleared the Airbus into position and hold.  I told the Captain we should start the second engine and he said we are waiting for the final weights as he did not see them laying on the pedestal ahead of the throttles.  I said no; we got them back at the gate; so we started the second engine and Tower told us to move up in the pad and stay on the left side.  I read back the clearance to Tower and went back heads down finishing my afterstart flow and starting the checklist.  As I was reading through the checklist ATC told us to stop and that we missed the hold point.  Tower then cleared the 737 for departure and then us.After airborne we discussed the event.  Looking back on it the Captain found the phraseology misleading as he thought the area between the holdshort lines was part of the pad; although nowhere on the 10-9 page is the word 'pad' used in that area.  Instead of saying pull up in the pad on the left side; if tower wanted us to move up further; I think a less confusing instruction would just be to 'pull up to the hold short line;' as Q is already on the left side.  I was busy running the checklist and did not think this would be an issue or find it confusing since we are both aware of the hot spot with two hold short lines and had done this exact taxi out to 8R last week.  Delaying the second engine start was a contributing factor as I was task saturated and lost situational awareness to complete my tasks inside the cockpit which took my awareness away from the outside.
[Report narrative contained no additional information.]
A320 flight crew described a runway incursion approaching Runway 8R at MIA. He was head down starting the second engine and reading checklists at the time.