I'm not a Microsoft employee so I can't speak for Microsoft, but I've researched this several times and asked Microsoft employees about it. The general rule is that IF you have a commercial version of Office (ie, not a Personal edition) you're permitted to create presentations and images using Office products using the supplied icons. How you use the presentations/images is up to you.
Microsoft's AI muddies the water by saying:
The images available in PowerPoint's icons are licensed for use within the Microsoft Office software only. They are not licensed for use outside of the software, such as on a website or in a corporate presentation.
If in doubt, it might be best to purchase royalty free icons/images from another source.
