The metre is the basic unit of length in the International System of Units (SI). It is defined as the distance light travels in a vacuum in 1/299,792,458 seconds. This precise definition helps ensure consistency in measurements across different fields, such as science and engineering. Originally, the metre was based on a physical object, specifically a metal bar kept in France. Today, it is used worldwide for measuring distances, heights, and lengths, making it a fundamental part of everyday life and various scientific applications, including those in physics and engineering.