String Gap

From YoYo Wiki

The Gap of a yoyo is the space between the two halves of the yoyo. Some yoyos have an adjustable gap allowing you to increase or decrease the size of this space. A larger gap makes yo-yos less responsive, and lowers drag from the string touching the sides of the yo-yo. A smaller gap makes yo-yos more responsive, and can also lower spin time by increasing drag on the sides of the yo-yo.