A shape is is said to have reflective symmetry if can be divided into two halves that are the same shape.

This can also be called line symmetry. The 'line' in this case is the line that divides it into two shapes that are themselves the same and can be matched up to each other. This is like putting a mirror to it, and the reflection that you get is the same as what is reflected. This line of symmetry is also called the axis of symmetry. Some shapes have more than one line or axis of symmetry. A square, for instance, has four lines of symmetry, but a rectangle has only two. These lines are shown in red in the diagrams.

There is another kind of symmetry as well, called rotational symmetry, but we will think about reflective symmetry first.