The vertical stroke rising above the line in minuscule letters like b, d, and h.
Most letters written in a minuscule script are confined between two lines on the page, but some letters -- especially the b, d, and h -- may contain a vertical stroke that rises above the line. This stroke is called the ascender. A thickened vertical stroke may be described as a clubbed ascender because of its shape. The size, appearance, shape, or direction of the ascenders can help classify the script.
Raymond Clemens and Timothy Graham, Introduction to Manuscript Studies (Ithaca, NY: Cornell University Press, 2007), 263.
Geoffrey Ashall Glaister. Encyclopedia of the Book, 2nd ed. (New Castle, DE: Oak Knoll Press; London: The British Library, 1996), 20.