Parallel lines are a fundamental concept in geometry. When two lines are parallel, it means that they never intersect or cross each other. They are always at the same distance apart from each other. This distance is equal at every point along the lines.

Key Points:
1. Definition of Parallel Lines: Parallel lines are two lines in a plane that never intersect or cross each other.
2. Distance between Parallel Lines: The distance between parallel lines is the same at every point along the lines.
3. Equal Distance: The distance between parallel lines is constant and does not change.
4. Visual Representation: Parallel lines can be represented by drawing two lines on a plane that never intersect and are equidistant from each other.

Explanation:
Parallel lines are often represented by using arrow marks on the lines. This indicates that the lines extend indefinitely in both directions without ever meeting or intersecting. When two lines are parallel, they have the same slope. The slope of a line determines its steepness and direction.

The distance between parallel lines remains constant because they never converge or diverge. This means that if we measure the distance between the lines at any point, it will be the same as any other point along the lines.

Parallel lines can be found in various real-life situations. For example, railroad tracks, the edges of a bookshelf, or the sides of a road are all examples of parallel lines. These lines are always equidistant from each other, which allows for smooth and consistent movement.

In summary, parallel lines are lines that never intersect and have equal distance between them at every point. They are a fundamental concept in geometry and have numerous real-life applications.