A subscript is a small number, letter, or symbol written slightly below the normal line of text. In the chemical formula H₂O (water), the small “2” is a subscript showing that each water molecule contains two hydrogen atoms. In math, you might see x₁ and x₂ (pronounced “x sub one” and “x sub two”) to distinguish between different variables.

Subscripts pack important information into a tiny space. Scientists use them constantly: CO₂ for carbon dioxide, C₆H₁₂O₆ for glucose. In math, if you're tracking multiple measurements over time, subscripts help keep them organized: you might write the first score as s₁, the second as s₂, and so on.

The opposite of a subscript is a superscript, which sits slightly above the line, like the small “2” in x² (x squared) or the “rd” in 3ʳᵈ. Both subscripts and superscripts are ways of adding extra information without cluttering up your writing. Think of them as whispered details that matter a lot: in H₂O versus H₂O₂, that tiny subscript makes all the difference between something you drink and something you use to clean a cut.