An optical isomer, also known as an enantiomer, is a type of stereoisomer that cannot be superimposed on its mirror image. This means that two optical isomers have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. This property is crucial in fields like pharmaceuticals, where different isomers can have vastly different biological effects. Optical isomers are characterized by their ability to rotate plane-polarized light in different directions. One isomer will rotate the light clockwise, known as dextrorotatory, while the other will rotate it counterclockwise, termed levorotatory. This optical activity is a key feature used to distinguish between the two forms in laboratory settings.