What are Presentation Files?

A presentation is to PowerPoint what a document is to Word or a worksheet is to Excel. In other words, a presentation is a file that you create with PowerPoint. Each presentation that you create is saved on your computer’s hard drive as a separate file.

PowerPoint 2010 presentations have the special extension .pptx added to the end of their filenames. For example, Sales Conference.pptx and
History Day.pptx are both valid PowerPoint filenames. When you type the filename for a new PowerPoint file, you don’t have to type the .pptx
extension, because PowerPoint automatically adds the extension for you. Windows may hide the .pptx extension, in which case a presentation file named Conference.pptx often appears as just Conference.

Versions of PowerPoint prior to 2007 saved presentations with the extension .ppt instead of .pptx. The x at the end of the new file extension denotes that the new file format is based on an open XML standard data format that makes it easier to exchange files among different programs. PowerPoint 2010 can still save files in the old .ppt format, but I recommend you do so only if you need to share presentations with people who haven’t yet upgraded to PowerPoint 2007. (You can download a program called the Microsoft Office Compatibility Pack from http://www.microsoft.com/ that enables PowerPoint 2002 or 2003 to read and write files in .pptx format. This program enables you to share your .pptx files with people who haven’t yet upgraded.)

PowerPoint is set up initially to save your presentation files in the My Documents folder, but you can store PowerPoint files in any folder of your
choice on your hard drive or on any other drive. You can write a presentation to a CD-RW drive or to a removable USB flash drive if you want to take it home with you to work on or if you need to give it to other people so they can use it on their computers.

See also:
Introducing PowerPoint Presentations 
What in Sam Hill Is PowerPoint?
What’s in a PowerPoint 2010 slide?

Passage reproduced from: http://powerpoint2010talk.blogdrive.com/archive/4.html