Graphics pixels, dpi, color depth
Since we spend a lot of time staring at monitors and printouts, what they actually are is important. Let's start by talking about your monitor:
First step - how many little dots of light are shown on-screen. Each of these dots is called a pixel. Older monitors can't display much:
These days, you have many options. See https://en.wikipedia.org/wiki/Display_resolution for more info about this. Most standard sized monitors these days (2018) are running somewhere around 2000x1000. Pity those uf us that started this game in CGA.
Second step - color. Or color depth. Or Bit depth. Basically, thenumber of bits used to indicate the color of a single pixel (https://en.wikipedia.org/wiki/Color_depth )
Third step: DPI (dots per inch). Another way to think about this is pixels per inch.
Time for a little math. The viewing area of my monitor is 13" across. I'm running it at 1024x768. So: 1024/13= 78.77. Or, effectively, 79dpi. Not super high, but good enough.