AquaTerm is a graphic renderer. In principle, this is a library with an API that allows various programming languages to display graphics on the screen. gnuplot is a charting utility. In many ways, gnuplot functions as a special programming language used to create graphs. He is able to record these graphs on a whole bunch of different devices ("terminals"). examples of some devices are files (png, pdf, postscript), printers and graphic libraries (X11, AquaTerm). Ultimately, any graph that you can make with gnuplot + AquaTerm to display on the backend can be done without gnuplot. Gnuplot's goal is to abstract away the details of the output device from the user as much as possible, so that if you create a plot and display it using AquaTerm, you can easily save this chart in a png file for future use. In reality, there is always terminal-dependent behavior, but in most cases it does not matter.