What is SharePoint Designer?

Even very competent and technically-minded people ask me what SharePoint is or what SharePoint Designer is. It is not an easy topic to explain. The following paragraph is how I would sum up SharePoint Designer:

SharePoint Designer fills in the space in the Office family that was vacated by Microsoft FrontPage (Microsoft's previous HTML editing program). It combines the familiar Office user interface, which was popular with users of FrontPage, with the power of Windows SharePoint Services and Microsoft Office SharePoint Server, allowing data and reports to be built into your SharePoint site easily with the help of task panes and templates.

This may sound a little obscure or like marketing speak and not really put you in the picture. Thankfully, like many things in life, it is easier to understand the concept when we see it in action, so let's dive into it and take a look.