Definition
Parallels are imaginary east-west circles drawn around the Earth parallel to the equator, used to measure latitude. Each parallel marks a specific angular distance north or south of the equator, expressed in degrees from 0° at the equator to 90° at the poles.
Plain English
Parallels are the horizontal lines you see on a globe or chart that run sideways around the Earth. They tell you how far north or south of the equator a place is.
Context Anchor
Seen in navigation, chart reading, and latitude-and-longitude position descriptions.
Derivation
From the Latin parallelus, meaning 'beside one another.' The lines are called parallels because they never meet — every line of latitude runs perfectly parallel to the equator and to every other parallel.
Why Pilots Care
Parallels give pilots a reliable way to determine their north-south position during flight planning and position fixes.
Intuition Check
Do not read parallels here as just “similar things.” In navigation, parallels are specific map lines used to measure north-south position from the equator.
Example Sentence 1
The 40th parallel runs through the northern United States, including parts of Colorado and Pennsylvania.
Example Sentence 2
Latitude increases as the aircraft flies north along successive parallels toward the pole.