Parallelism refers to two or more lines or planes in Euclidean space that do not intersect. Euclid's parallel postulate states that given a line and a point not on the line, there is exactly one line through the point that is parallel to the given line. Two lines are parallel if they remain an equal distance apart and never intersect. In elliptic geometry on a sphere, all lines are great circles that intersect, so there are no parallel lines. In hyperbolic geometry using the Poincare disc model, lines are represented by arcs of circles orthogonal to the boundary circle.