What does Bump mean in these FS threads?
Each time a post is made in a thread, the thread is "bumped" up to the beginning of the list of threads with New Posts in them.
Many people use the New Posts function to organize their visits to Photrio, so "bumping" a thread attracts their attention.
The member who started the thread is thus able to encourage attention to it.
There is an expectation that "bumping" will be done with reasonable rather than excessive frequency.
Any post will serve to bump a thread. So if you prefer, you could post "Happy holidays" or "Go Ajax" if you prefer - although the latter might not be understood by everyone