An axis is an imaginary line that serves as a reference point for rotation or measurement. In geometry, it often refers to a straight line around which an object rotates, such as the Earth's axis, which is tilted and causes the changing seasons. In graphs, the x-axis and y-axis are used to plot points and visualize data. In mathematics, the term "axis" can also refer to the central line of symmetry in shapes. For example, in a circle, the axis runs through the center, dividing it into equal halves. Understanding axes is essential in various fields, including physics, engineering, and computer graphics.