1. Meaning:
Be loved very much by someone.
If someone is the apple of your eye, you think he/she is very important to you, and you love him/her
very much.
This idiom is used especially when someone is loved by an older member of his/her family.
Example:
Erika is Mark's only granddaughter, and she's the apple of his eye.
Sarah's only son was the apple of her eye.