adjective
Definition: Relating to lenses or glasses that have two different optical powers, one for seeing far away and another for seeing close up.
Example: She wears bifocal glasses to help her see both the computer screen and the board at the front of the classroom.
noun
Definition: A type of eyeglass lens that has two different optical powers, allowing the wearer to see clearly at both near and far distances.
Example: He needs bifocals to read and drive without changing glasses.