I don't think think there is a strict meaning to it really, it was used to describe the Geophagine tribe back when they were all/mostly in the Geophagus genus. In the strictest sense, you could use it for the species in the Geophagus genus.
In the broader sense, you could use it for the entire Geophagine family.
Typically though, most people leave out some Geophagine groups like pikes, apistos, Apistogrammoides, Taenicara, and Dicrossus ...
which usually leaves Geophagus, Satanoperca, Gymnogeophagus, Biotodoma, Microgeophagus, Guianacara, the red hump complex, the brasilinesis complex, and heckelii ... as these are the species most likely to actually sift or at least pick at the substrate.