Explanation:
Optical isomers, also known as enantiomers, are a type of stereoisomer. They have the same molecular formula and connectivity but differ in the way their atoms are arranged in space.

Definition of optical isomers:
Optical isomers are molecules that are non-superimposable mirror images of each other. They have the same physical and chemical properties except for their interaction with plane-polarized light. Due to their mirror-image nature, they rotate plane-polarized light in opposite directions. One enantiomer rotates the light clockwise and is referred to as (+) or dextrorotatory, while the other rotates the light counterclockwise and is referred to as (-) or levorotatory.

Comparison with other types of isomers:
a) Structural isomers: Structural isomers have the same molecular formula but differ in the arrangement of their atoms. They have different connectivity and may have different physical and chemical properties.
b) Facial isomers: Facial isomers are a type of stereoisomer where the ligands attached to a central metal atom are arranged in a specific way. They can be cis or trans isomers depending on the arrangement of ligands.
c) Meridional isomers: Meridional isomers are a type of stereoisomer in coordination compounds where the ligands attached to a central metal atom are arranged in a meridian plane. They can be cis or trans isomers depending on the arrangement of ligands.

Conclusion:
Optical isomers, also known as enantiomers, are a type of stereoisomer that are non-superimposable mirror images of each other. They have the same physical and chemical properties except for their interaction with plane-polarized light. It is important to distinguish optical isomers from other types of isomers such as structural isomers, facial isomers, and meridional isomers, as they differ in the way their atoms are arranged in space.