What does the instruction "Climb heading [BEARING] to [NAVAID] 2.5 DME" mean? I am examining FAA's Standard Instrument Departure Procedures (SIDs) and while reading their textual description, I came across this instruction from 
LGA's La Guardia Five Departure SID, for Runway 13 (Whitestone climb): "Climb right turn heading 180 degrees to LGA 2.5 DME then left turn heading 040 degrees etc."

Could someone explain to me what the phrase "heading to LGA 2.5 DME" means? Does it mean that the pilot maintains this magnetic bearing (180 degrees) until the distance between the aircraft and the LGA (NavAid) becomes 2.5 nautical miles?
DME is "Distance Measuring Equipment". It tells you how far you are from the equipment transmitting the signal. This is often co-located with a VOR, or at an airport.


  turn heading 180 degrees to LGA 2.5 DME


So, this means turn due south and continue until you are 2.5 nautical miles from LGA. At this point you're instructed to turn left on to a heading of 040.