Geoweb, web mapping, web gis, ppgis, pgis, VGI or some form or another of these terms. There isn't really a great way to differentiate them, but I have my own little interpretation (I need to, grad student in Geography here).
Geoweb: Location-aware web-based applications. These can be simply the auto-locate closest server background apps run by Google, the Yelp.com search results (always something near your location), etc.
Web Mapping: Web-based applications that allow the presentation or creation of maps. Google Maps, Bing Maps, Mapquest, etc are parts of the web mapping sphere.
Web GIS: A GIS implemented using the web or internet technologies to connect the multiple parts (storage, presentation, analysis). Notice that web mapping is a subset of web GIS, as it only provides storage and presentation (directions, while a sort of analysis, is not the only analysis needed to make a GIS).
(Public) Participatoy GIS: The long dream of Humanists in Geography, where a participatory process is driving the components of GIS (including storage, presentation and analysis). No one has a clear understanding what this would look like or what it is. If you want to open the participatory process, you can put the extra P in the front (Public).
Volunteer Geographic Information: The clearest part of (P)PGIS thus far: participatory data gathering. This is where you enable the collection of data to be participatory, like the OpenStreetMap project. Of course, the process is not completely PPGIS yet, as the data collection is indeed open, but cleanup, storage, dissemination and maintenance are not as open as one would hope.