In the paper "Calibrating Noise to Sensitivity in Private Data Analysis" by Dwork et al., the term "statistical difference" is used as following (in page 280):
Finally, if a $1 − \gamma$ fraction of the $z$’s are $\delta$-good for a particular pair $(r, b)$, then the statistical difference between the distribution $p'(z)$ and $p(z)$ is at most $2(\gamma + \delta)$.
where $\delta$-good is defined as:
A value $z$ is $\delta$-good for a pair $(r, b)$ if $p'(z) − p(z) \leq \delta · p(z)$.
What is the term "statistical difference" as used in this paper? It seems it is not defined anywhere else in the paper and it is used as if something well-known.