HTML <sub> Tag

The <sub> tag in HTML is used to define subscript text, which appears slightly below the baseline of the surrounding text. Subscripts are commonly used in mathematical expressions, chemical formulas, and scientific notation to indicate things like chemical elements (H₂O), mathematical indices (x₁, x₂), or other specialized notation where characters need to appear lower than the normal text line.

Visually, the <sub> tag decreases the vertical position of the text and usually reduces its font size slightly compared to the surrounding content, though exact rendering can depend on the browser and applied CSS. The tag does not carry semantic meaning beyond marking text as subscript; it is purely presentational.

Example usage:

<p>The chemical formula for water is H<sub>2</sub>O.</p>
<p>In mathematics, the first term of a sequence is denoted as a<sub>1</sub>.</p>

In these examples, the numbers "2" and "1" are rendered lower than the main text, making them subscript. The <sub> tag can be used inline with other text and can be nested inside other elements such as <span> or <p>.

Key points:

• Inline element
• Displays text below the baseline
• Typically used in scientific, mathematical, or technical contexts
• Reduces font size slightly by default (but can be overridden with CSS)