"Bone-centered" is a very important term in China's calligraphy, which refers to the vigorous and straight stippling in the process of writing. This kind of brushwork requires that the strokes always run in the center of stippling, thus making stippling more powerful and backbone.
In calligraphy, the center is not an independent brushwork, but is often used with other brushwork. For example, when writing regular script, the central vertical bone can be used with strokes such as side attack and counterattack to make the font more varied.