1. A property of two or more lines that is separated at all points by the same distance. 2. A horizontal line encircling the Earth at a constant latitude. Parallel is a degree of latitude that circles the earth parallel to the Equator.So the Equator is a parallel whose latitude is 0. Measures of latitude range from 0 to 90 north of the Equator and from 0 to -90 to the south.