Microsoft PowerPoint is a presentation tool included with Microsoft Office. PowerPoint allows you to make interactive multimedia slideshows to present information. When you open a PowerPoint Presentation (.ppt, .pptx), the PowerPoint software is launched, but the presentation doesn't start automatically. PowerPoint Shows on the other hand start immediately in full screen mode to provide a more polished and professional experience.
PPSX PowerPoint Shows are different than the PPS version in that they use the Microsoft Office Open XML format. The Open XML format makes it easy for other programs, such as OpenOffice.org, to read PPSX files (and other Open XML file types). The Open XML format was introduced with Microsoft Office 2007.