What are guest users in Skype conversations?
Guest users are a new feature for Skype for Web, allowing you to have conversations with friends regardless of whether they are on Skype. They are a temporary account, good for 24 hours, and specific to the one conversation they've been invited to. You cannot add them as a contact or send them a one on one message, as they won't get delivered. Also once that conversation window is closed, their account will automatically expire.