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 $$\begin{equation} X \overset{d}{=} |G| \end{equation}$$