Mirror surface

...The inversion shown in Figure 11 is the inversion itself, and this symmetric element is called the center of symmetry.
[Mirror symmetry]
Also, when a figure has a symmetry, the part of the figure on the side of the plane that passes through the point of inversion and is perpendicular to the axis of reflection is reflected by that plane, so the symmetry element is called a mirror plane, and in this case it is represented by m, for mirror, instead of m .
[Helical symmetry]
In addition, a spiral, which is a combination of a rotation and a translation along the axis of rotation, can also be a symmetry operation for a crystal structure.

*Some of the terminology explanations that mention "mirror surface" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…図11で示すは反転そのものであり，この対称要素は対称心とよばれる。
［鏡映対称］
　また図形がをもつと，それは反転の点を通って回反軸に垂直な面の側の図形の部分が，他の側の部分をその面で映したような関係になっているので，その対称要素は鏡映面とよばれ，この場合はの代りに鏡mirrorのmで表す。
［らせん対称］
　さらに，回転と回転軸の方向の並進tとの合成であるらせん(螺旋)も結晶構造の対称操作となりうる。…

※「鏡映面」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報