A number line is a straight line that represents numbers in a sequential order. It typically has arrows on both ends to indicate that numbers continue infinitely in both directions. Each point on the line corresponds to a number, with equal spacing between them. The center of the number line usually represents zero, with positive numbers extending to the right and negative numbers extending to the left. Number lines are useful for visualizing mathematical concepts such as addition, subtraction, and fractions. They help in understanding the relationships between numbers, making it easier to compare values and perform calculations. Teachers often use number lines in classrooms to aid students in grasping these concepts.