A slidecast is a slide presentation with synchronized audio, and Slideshare.net is an Internet service for creating and sharing slidecasts. As shown here, the user can watch continuously or skip from slide to slide using the viewer controls.
One creates a slidecast by uploading a PowerPoint, PDF or OpenOffice presentation with the slides and an mp3 file with the audio track. The site provides editing tools for selecting and adjusting the portion of the audio file to play with each slide. You can see how it is done in this how-to screencast.
The slideshare site also has the features of a typical social networking site, allowing viewers to comment on, evaluate and search for slideshows. You can also upload and share a slide presentation with no audio track.
Do some of your professors use slide presentations in class? Would it be helpful to have them available for viewing after class as slidecasts? Have you made a presentation that you could have recorded as a slidecast?