Before revision: The sub-fractional Brownian motion (sfBm) could be considered as the intermediate step between the standard Brownian motion (Bm) and the fractional Brownian motion (fBm).
After revision: The sub-fractional Brownian motion is a stochastic process, characterized by non-stationarity in their increments and long-range dependency, considered as an intermediate step between the standard Brownian motion (Bm) and the fractional Brownian motion (fBm).