What is the blue pin?

I'm a recent convert and am using a training book to learn iWork. I'm currently doing a newsletter lesson for Pages and am having a problem that I can't find an answer for. As part of the lesson, I've pasted a chart from Numbers into my newsletter. I'm trying to resize and move the chart but it isn't responding as expected. I've noticed a blue pin just beloe the bottom left corner of the selection box. The blue pin is only seen when the chart is selected.

I can't find any info on the blue pin -- not in help, the user guide, this forum, or in googling. I wish I could post a screenshot of it. I suspect it has pinned the chart to the page and that is why it resists moving and resizing, but I can't find anyway to 'unpin' or change the pin color or delete it.

Can anyone help me?