a small fold or band of tissue that restricts the movement of an organ or part, such as the fold under the tongue (lingual frenum) or between the lip and gum (labial frenum).

器官や部位の動きを制限する小さなひだ状の組織（例: 舌下のひだ＝舌小帯、唇と歯肉の間のひだ＝口唇小帯）

archaic or figurative: a restraint or bridle (original literal sense from Latin).

古語的・比喩的：抑制や手綱（ラテン語本来の意味から）