abscissa : x-coordinate.
ordinate : y-coordinate.

world coordinates : real world coordinates like 15 gm or 100 lb.
view coordinates  : screen coordinates defined in terms of pixels.

A pixel is the smallest addressable unit of the display buffer. Display buffer is an area
which contains the color values of all the pixels on the screen.

there are 4 primitives in pgplot : lines, graph-makers, text, area fill.

clipping means to cut off part of an image/drawing at the viewport boundry. This is done so that part of an image should NOT clutter an image in the other viewports. Clipping is an inherent feature of all the windowing systems.

a polyline is a continuous set of segments. e.g. a line from (0,0) to (1,1) to (5,3) is a polyline having two segments.

buffering is a method of drawing a set of items together(at once) on the viewport instead o being drawn one-by-one. All the graphical items are stored in the buffer and the buffer is then output on the viewport.