Font embedding on the web
If you use a graphic application to create a logo, heading or other graphics for a web site, that's not font embedding. On a web site, fonts are embedded in order to replace the default fonts for text or headlines. Embedded fonts require a different font format and a different type of license. When you add a font to your shopping cart, you can choose a web license. After purchasing, you'll receive web-ready fonts in various formats and some sample CSS code to help you get the fonts working on your site.
Web Typography on Wikipedia
Product creation on the web
If your website allows users to create posters, t-shirts, lolcats, photo captions, stickers etc, a custom license
Font embedding in documents
With the regular (desktop) license, you're allowed to embed fonts in PDF documents for viewing and printing, but not for editing. If someone at a remote location wants to edit a document which contains embedded fonts, they must purchase their own license. Internal corporate documents with embedded fonts may of course be edited on licensed workstations. With the regular (desktop) license, you're allowed to embed fonts in DOC, DOCX and various OpenDocument formats such as ODT.
Font embedding in eBooks
If you're using fonts to create a cover, illustrations or heading graphics, the regular (desktop) license is sufficient. If you want to embed the fonts into an eBook in order to replace the existing text or heading fonts, you can purchase an eBook embedding license. Use the Fontspring link on the font you'd like and you'll find an eBook license option.