A Gleam in One’s Eye

What does the idiom “a gleam in one’s eye” mean?

Definition: 1) An expression of suppressed amusement; an expression showing that one is keeping a secret; 2) a future event, especially the birth of a child, that one has not yet even considered

Example: 1) You always have a gleam in your eye when I talk about Jenna and Bob. Do you know something I don’t know? 2) When that song was recorded, you weren’t even a gleam in your mother’s eye.