A (1-)locus is defined by Joyal to be a locally presentable category $C$ (generated by a small set of compact objects under colimits) with a zero object such that collections of objects in $C$ indexed over sets (denoted Fam($C$)) form a Grothendieck topos.

The nlab page (which briefly discusses the $\infty$-categorical analog) is here: https://ncatlab.org/nlab/show/locus

An example of a locus is the category of pointed sets (Fam($Set_{\bullet}$) is equivalent to the category of presheaves on the walking-arrow-equipped-with-a-section).

What are some other examples of loci? I couldn't find any literature on the topic (probably because it is a very new notion)