A straight line is the shortest distance between two points in a plane. It extends infinitely in both directions and has no curves or bends. In geometry, straight lines are often represented by equations, such as y = mx + b, where m is the slope and b is the y-intercept. Straight lines can be classified into different types based on their orientation. For example, a horizontal line runs parallel to the x-axis, while a vertical line runs parallel to the y-axis. These lines are fundamental in various fields, including mathematics, physics, and engineering, as they help describe relationships and patterns.