A circular form at the end of the arm in letters.
Definition: In typography, the terminal is a type of curve. Many sources consider a terminal to be just the end (straight or curved) of any stroke that doesn’t include a serif (which can include serif fonts, such as the little stroke at the end of “n” as shown in the illustration). Some curved bits of tails, links, ears, and loops are considered terminals using the broader definition (see the Microsoft Typography site for further explanation).
Ball terminal is a combination of a dot (tail dot) or circular stroke and the curved bit (hook) at the end of some tails and the end of some arms (a, c, f). Beak terminal refers to the sharp spur or beak at the end of a letterform’s arm and the curved bit (terminal) between the beak and the arm.
A ball terminal is a design feature of a typeface or glyph where the end of a stroke takes a roughly circular shape, as opposed to a serif or a square end.