If every hinge point of a fold in profile are connected, we can get an imaginary plane which divides the fold symmetrically. This imaginary plane is known as axial plane. The geometrical characteristics are used to classify folds.

• 如果在横断面上将一个褶曲各弯曲层上的枢纽点连接起来，便可得到一个对称分隔褶曲的标志面，这个标志面叫做褶皱轴面，可以用褶皱轴面的几何学特征来作褶皱分类。