A more thorough explanation:

Definition: able to be seen or noticed; clear and obvious.

Examples:

• The stars were visible in the night sky.
• The writing on the board was not visible from the back of the classroom.
• The stain on the shirt was visible even after washing it.

The examples illustrate that something that is visible can be seen or noticed with the eyes. The stars in the night sky are visible because they can be seen by the naked eye. The writing on the board may not be visible to everyone in the classroom because of their distance from it. The stain on the shirt is visible because it can be noticed even after washing it.