Luella,
"Members Gallery" is the
vBGallery term for a Gallery category that is configured to automatically create new sub-categories based upon the user name. For example, on my personal site I have a category named Creative Imaginations that has the "Act as Members Category" option turned on. When a user then uploads a file to that category it will be automatically grouped togeter under a sub-category with the user name being the name of the sub-category (
example). You can then go further and allow your users to create sub-categories within a Members Gallery category to allow yours users to manage their own 'albums' in the category (
example). Check
this thread for a bit more in-depth reading and instructions on how to turn the options on.
In
PhotoPost PHP Pro, though, it has a slightly different meaning which I'll leave to one of the PHP Pro guys to explain.