Let $G \in \text{Gaussian}(\mu, \sigma)$ be a D210: Gaussian random real number.
A D3161: Random real number $X \in \text{Random}(\mathbb{R})$ is a folded gaussian random unsigned real number with parameter $(\mu, \sigma)$ if and only if
\begin{equation}
X
\overset{d}{=} |G|
\end{equation}