It’s an object defining a text or a color-filled rectangle.
Define a text the main edit field.
Choose the font attributes (type, color, size, etc.) by pressing the Font… buton.
Check Border if you want that the text window to be bordered.
You can check Filled and choose the background color by pressing the Background Color….
Use such objects in order to create more specific control panels, with a better graphical appearance.
See also: