Lync started out as "Office Communicator 2007" before being renamed Lync. Then Microsoft purchased Skype and rebranded Lync as "Skype for Business" even though it was still a completely unrelated product, with just some basic interoperability slapped on. Skype-the-consumer-app lived on separately as its original product in parallel.

Just another example of how Microsoft is utterly incompetent at branding - always have been and always will be.