subscript; subscript character
Computing term for a character printed slightly below the normal line, such as the '2' in H₂O.
Subscript characters are often used in chemical formulas.
上付き文字 is a superscript character, printed slightly above the normal line, while 下付き文字 is a subscript character printed below.
Compound of 下付き (したつき, 'attached below') + 文字 (もじ, 'character').