What, Exactly, Are Social Skills?

We always hear this vague idea that it’s important for people (especially children) to develop social skills. They are apparently so important that acquiring them is often used as a justification for public (or private) schools over against the general academic superiority of home schooling. But talking about whether they matter last week made me start wondering exactly what they are. This is important for any discussion of various educational objectives, but I think getting clarity on social skills is also necessary for anyone simply parenting children. So, today, I’d like to just get a better picture of what social skills are (as compared with, say, physical skills or intellectual skills).