Exponential Moving Average
Is a [see page 16, way] of measuring the average of a collection of values, as the values are calculated (as opposed to calculating all of them and then averaging at the end).
\begin{align}
\label{eq:original}
\tau \frac{\Delta \bar{x}}{\Delta t} &= - \bar{x} + x \
\label{eq:eulers-method}
\bar{x}_{n+1} - \bar{x}_n &= - \frac{\Delta t}{\tau} \bar{x}_n + \frac{\Delta t}{\tau} x_n \
\bar{x}_{n+1} &= ( 1 - \frac{\Delta t}{\tau} ) \bar{x}_n + \frac{\Delta t}{\tau} x_n \
\bar{x}_{n+1} &= (1 - \alpha) \bar{x}_n + \alpha x_n
\end{align}
This is called an EMA because the left hand side of eq:original is an exponential.