Definition
A compound/substance that can rotate a plane-polarized light is called an optically active compound/substance.
Explanation
Optically active substances have a chiral carbon and no plane of symmetry.
Optically Active
In one sentence
A compound/substance that can rotate a plane-polarized light is called an optically active compound/substance.
Terms used on this page
Every one of these links to a full definition with an example.