"Old School Renaissance" in this case, the revival of zine-style RPGs influenced directly by Basic+Expert DnD from the late 70s and early 80s. The term has been diluted somewhat from the original blog scene of the 2010s (ish), with some games being near-perfect clones of BX DnD like Old School Essentials to extremely rules-thin games that are almost better enjoyed as art projects (Mork Borg, Ultraviolet Grasslands) and everything between.