canvas
  The scrollable grid in the main window. The widgets are dragged into cells of the grid. Not to be confused with the 'canvas' widget.
cell
  A cell is the intersection of a single row or column.
cavity
  A cavity is one or more cells, in a rectangular region. Only one widget may occupy a cavity, and unless the widget has been configured to fill its cavity, much of it will appear empty. Grid lines will not pass through a cavity, only around its edges.
column
  A column is the space between vertical grid lines. In the context of a widget, its column represents the left most column in its cavity. Columns are numbered starting at one (1).
column-span
  A column-span is the number of columns occupied by a widget.
option sheet
  Each widget has a list of name/value pairs that specify all the needed to specify the properties of that widget. This list of name/value pairs is called a property sheet, which is accessed by double-clicking on the widget.
grid
  The grid demarcates the set of rows and columns for the interface, dividing it into cells into which widgets may be placed.
item_name
  This is the name the application uses to access a widget. If the widget's procedure is instantiated by `project_ui $frame`, then the full name of the widget is `$frame.item_name`
palette
  The palette is the column of buttons on the left side of the user interface that indicated the widgets. Widgets are created by clicking on a palette item, and dragging it onto the desired location on the canvas.
panel
  A panel consists of all the widgets created together on the canvas at one time. Panels are saved as a single `ui` file, and are instantiated by calling the panel's procedure with the name of the frame (or toplevel) it is to be rendered in. A typical application consists of one or more panels.
row
  A row is the space between horizontal grid lines. In the context of a widget, its horizontal represents the top most column in its cavity. Rows are numbered starting at one (1).
row-span
  A Row-span is the number of rows occupied by a widget.
tool-bar
  The tool-bar is the row of icons and menus along the top of the user interface, just under the menu bar, that provides a short cut for setting common properties for the selected widget.
sub-grid
  A sub-grid is a table of rows and columns that occupies a cavity either in the main grid, or in another sub-grid. Sub-grids, which are created by dragging frames onto the existing grid, are used when the programmer needs to give some widgets a different resize behavior.
widget
  A widget is an atomic user interface element, such as a button or scrollbar. All of the available widgets are presented on the palette.