The second dimension is commonly referred to as **2D** or **two-dimensional**. In this context, it refers to a plane or surface where only two measurements are needed to specify a position: typically **length** and **width** (or **x** and **y** coordinates in a Cartesian coordinate system).
In terms of geometry and physics, a 2D object can be thought of as a flat shape that exists in a space with two degrees of freedom. Common examples of 2D shapes include squares, circles, and triangles. These objects have no depth or height and can be represented visually on paper or a screen as flat images.
To summarize:
- **The second dimension** refers to the two-dimensional space where objects have length and width but no depth.
- **2D objects** are flat shapes like squares, rectangles, and circles.