Slideshows are much more than just a random collection of pictures. In fact they are much more than a connected collection of pictures.
By definition they are a group of pictures viewed in a sequence. They can however be used to convey messages, advertise products, illustrate ideas and demonstrate artistic content among other things.
They can be as simple as a WordPress slideshow:
They can have Musical backgrounds:
They can even be complete elaborate productions advertising a product or an event like this commercial for the Journalism Education Association National Convention produced by Brian Snyder of the Walter Cronkite School of Journalism and Mass Communication.
E-dreamconsulting 
Dave, the AEJMC promo is more of a video piece than a photo slideshow though.
Technically true. In class we started with traditional advance on click sideshows. Then put them in a timeline adding V/O and music. We then added video footage, nat sound and sound bites. Finally we migrated to video only.
I find it easier to teach video editing using this scaffolded progression and the same editor.
FYI
I am a big fan of Brian Storm. He is a wonderful story teller who uses everything at his disposal that is appropriate to the story. http://mediastorm.com/