Holding short...

Here is a picture of airport markings on a taxiway coming up on a runway. From Wikipedia, the free encyclopedia: A taxiway is a path on an airport connecting runways with ramps, hangars, terminals and other facilities. A runway (RWY) is a strip of land on an airport, on which aircraft can take off and land. Runways may be a man-made surface (often asphalt, concrete, or a mixture of both) or a natural surface (grass, dirt, or gravel).

(p.s. I think airports are gorgeous at night - but it makes it difficult to take pictures)

Pilots must have permission from Air Traffic Controllers to move anywhere on the airport surface. We call Ground Control and let them know when we want to taxi to the runway. When we are close to the departure end of the active runway, we switch to the tower control frequency to get clearance to enter the runway and hold in position or to immediately takeoff.

There has always been trouble with pilots missing these markings and entering an active taxiway or misreading them (you have to "dash" across the dashes to get off the runway) and becoming a hazard to someone taking off. During low visibility conditions, some airports have lights that draw attention to these makings.

A great description of what I'm talking about is from The VATUSA Training Department, which exists to:
Work in conjunction with ARTCC's to select and maintain Training Administrators.
Establish a set of training guidelines, to ensure all members are held to the same standards.
Establish and maintain study guides for member use.
Establish and maintain written examinations, to ensure all members are at the same level.
Work In Conjunction with the ARTCC's to develop an all-inclusive ARTCC specific training program. http://www.vatusa.org/training/index.html

Ground Control is responsible for the airport "movement" areas, or areas not released to the airlines or other users. This generally includes all taxiways, holding areas, and some transitional aprons or intersections where aircraft arrive having vacated the runway and departure gates. Exact areas and control responsibilities are clearly defined in local documents and agreements at each airport. In the real world any aircraft, vehicle, or person walking or working in these areas is required to have clearance from the ground controller. Ground control is vital to the smooth operation of the airport because this position might constrain the order in which the aircraft will be sequenced to depart, which can affect the safety and efficiency of the airport's operation. In real-life, Ground Control and Local Control (TWR) are located next to each other in the Tower Cab. They can communicate by visual signals or simply speaking to each other. They control aircraft based primarily on what they see out the windows.

The Airplane Owners and Pilots Association puts out Safety Advisories to help pilots with critical safety issues. If you'd like to read more, their flyer can be read here: http://www.awp.faa.gov/ops/runway_safety/education/safety%20advisor%20towered%20airports.pdf