There are so many names for 'Families' that it is confusing. I'm going to try and make sense of it here. I'll add on as I find new ones. Please feel free to comment:
Family: In Revit you can go to the Insert menu and 'Load Family'.
Components: Looks like this is what Autodesk is mostly calling 'Loadable Familes' inside of Revit.
Component Families: A variation of Components I've seen
Loadable Families: Refers to things like doors which you insert. Found this in the Autodesk 2010 Family Guide.
In-Place families: Nowhere in Revit, that I can see, does it ever say 'In-Place Families'. All I have found is Component-Model In-Place.
System Families: Also referred to as 'Types'.
'Wall etc' Types: System Familes. These can be loaded in through Manage-Settings-Transfer Project Standards
Styles: Sometimes this refers to annotation System Families. I've seen this describing Types as well.
Content: Usually refers to all Families in general.
Detail Components: Annotation Family
Symbol: Annotation Family which scales with the view
When it comes right down to it, pretty much everything is a 'Family' in Revit. I would like to see a little more consistency with these things. Not all the blame rests on Autodesk but I think that they are in a position to help this kind of thing.