Definition
Rotational symmetry
A figure has rotational symmetry when a turn smaller than a full turn makes it match itself.
What it means
Keep the figure's centre fixed and turn it. If the whole figure fits exactly onto its starting shape before completing a full turn, it has rotational symmetry. The order counts all matching positions in one full turn, including the starting position.
Remember it
Turn around one centre; match before the full turn ends.
Example
A non-square rectangle matches itself after a 180° turn about its centre. In one full turn it matches in two positions, so its rotational symmetry has order 2.
Watch for
Matching only after 360° does not count, because every figure returns after a full turn.
Common mix-up
The centre and angle matter; sliding or reflecting the figure does not test rotational symmetry.
Exact meaning
A figure has rotational symmetry if a rotation about a fixed centre through an angle greater than 0° and less than 360° maps the figure onto itself.