\={a}The symbol \={a} is used to denote the letter 'a' with a macron accent over it. In mathematical typesetting, this is often used to represent a mean or average value, or to indicate a specific modified variable.
Using \={x} to denote the mean of a set of values.
\text{The mean of } x_1, x_2, \ldots, x_n \text{ is } \=xUsing \={a} to indicate a long vowel sound in phonetic transcription.
\text{In linguistics, } \={a} \text{ represents a long 'a' sound}Using \={a} to denote an adjusted or modified version of a variable.
\text{Let } \=a \text{ be the adjusted value of } a