First, 27L is one of three east-west runways used simultaneously for daytime arrivals in "West Flow", when winds are from the west and aircraft land from east to west into the headwind. Runways 27R and 28C are also used in this configuration.

In aviation, "27L" refers to the specific orientation and position of a runway. The number "27" represents the magnetic heading of the runway rounded to the nearest ten degrees and then truncated; thus, a plane landing on runway 27 is facing 270 degrees, which is due West. The "L" stands for "Left," indicating that there is at least one other parallel runway (likely a 27R or 27C) to its right. This naming convention is vital for pilot navigation and air traffic control to prevent "runway incursions." If you were to turn around and use the same strip of asphalt in the opposite direction, it would be labeled 09R (090 degrees/East), because the opposite of 270° is 90°, and the "Left" side becomes the "Right" side from the reverse perspective. This system ensures clarity regardless of which direction the wind requires the planes to fly.