In geometry, parallel lines are lines in a plane which dae nae meet. The assumed existence an properties o parallel lines are the basis o Euclid's parallel postulate. Twa lines in a plane that dae nae intersect or touch at ony pynt are said tae be parallel. Bi extension, a line an a plane, or twa planes, in three-dimensional Euclidean space that dae nae share a pynt are said tae be parallel.
Parallelism is primarily a property o Euclidean space an some relatit geometries such as affine geometry. Some ither spaces, such as hyperbolic space hae analogous properties an aa sometimed referred tae as parallelism.