HTML subscript is a tag that allows you to create text that appears below the baseline of the surrounding text. This can be useful for creating mathematical or chemical formulas, as well as for other occasions where you want to include small text next to regular text.

To create HTML subscript text, you use the <sub> tag. This tag is placed around the text that you want to appear as subscript. For example, if we wanted to create a formula for water using HTML subscript, we would write:

Water = H<sub>2</sub>O

This would display on a web page as:

Water = H2O