A torsion angle is a measure of the angle between two planes formed by four atoms in a molecule. It is important in understanding the three-dimensional shape of molecules, particularly in organic chemistry and biochemistry. The torsion angle helps determine how flexible or rigid a molecule is, influencing its reactivity and interactions with other molecules. In a molecular structure, the torsion angle is defined by the rotation around a bond connecting two atoms. This angle can affect the overall conformation of the molecule, impacting properties such as stability and biological activity. Understanding torsion angles is crucial in fields like drug design and protein folding.