This is the 4099th most frequent Japanese word.
ボールペン
Ballpoint pen.
Here, 「ボールペン」 (ballpoint pen) is used to specify the object employed in an action (writing).
私は赤いボールペンを使って書きます。
I write using a red ballpoint pen.
In this sentence, 「ボールペン」 represents the subject of the existence statement (an item that is present on the desk).
机の上にボールペンがあります。
There is a ballpoint pen on the desk.
Here, 「ボールペン」 acts as the item being transferred or gifted from one person to another.