Ha ha... I was thinking it would just be any program capable of generating the original base mesh. I worked with a couple modelers before sub-division was ubiquitous, Modeler 3D (which evolved into Lightwave's Modeler) was especially basic. You selected your work "plane" in one of the three windows and added individual points in another window. Technically you could make anything this way (if you had the time and patience of course).
Here's how I look at it... Basic modeling functions are things like: Load/create primitive.. lathe/extrude.. boolean cutting/joining.. point/edge/face tools.. While bone creation, skinning, weighting... All of that is specific to rigging animated characters. Most programs of Poser's complexity have basic modeling tools. But if you simply want to know what constitutes a modeling program (vs. a sculpting program or general purpose program) take a look at one of the number of programs which only focus on modeling: http://www.wings3d.com/ https://www.inivis.com/ http://www.metaseq.net/en/