I came across this annoying moment while writing a how-to article and realized I didn't know the name of those white squares that surround views.
Here some images for clarification.
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I typically call them "control points".
Here are some web references that use similar terminology.
you can also use the onscreen control points to resize the rectangle
An article on resizing graphics in CS5
In the default scaling mode, the selection scales graphic elements from the control point opposite the one you’re dragging.
When you hover your mouse cursor over a cell or table edge, the boundary turns blue, indicating a layout area. Click this boundary and control points appear.... You can click and drag these points to resize....
I agree with the comment by Steve Rindsberg that mentioned that the preferred terminology might vary by application and will note that Microsoft's documentation on Powerpoint appears to use control point for Bezier curves and resize handle (as suggested by hBy2Py) for resizing.