In form, report, and data access page Design view, one of the small squares displayed on the edge of a selected control that you click and drag to resize the control.
Form or report sizing handles
Data access page sizing handles
In data access pages, you can’t resize a list box or drop-down list box vertically. The vertical size of list boxes and drop-down list boxes is based on the font setting of the control.
Note The large square in the upper-left corner of the selected control is a move handle, not a sizing handle.