A small letter or number placed slightly lower than the normal text.

Examples:

• the number 1 here: **A _{1}** (pronounced "A sub 1" or just "A 1")

• the letter m here:

**x**(pronounced "x sub m" or just "x m")

_{m}Often used when we have a list of values.

Example: Average = (x

_{1}+ x

_{2}+ x

_{3}+ ... + x

_{n})/n

(Which means to add all x values, from 1 to n, then divide by n)

Note: when the letter is up high it is a "superscript".