Key repeat is the term used to describe the behavior of our keyboard that will repeat the key we pressed with a certain rate.
Once you know, it comes automatically for you to realize that the rate of deletion while pressing Delete key as well as the speed of moving cursor with Arrow Keys are set by this Key Repeat Rate.
There is this nice thing in Mac that we, as a mere human, can adjust the Key Repeat Rate without much effort. It’s just about moving a slider or two from left to right (or vice versa).
These two sliders, named Key Repeat Rate and Delay Until Repeat, are concealed inside System Preferences ▸ Keyboard & Mouse ▸ Keyboard. Key Repeat Rate will handle the delay between that very same letters while Delay Until Repeat will manage the delay needed to begin letters repetition.
I feel my Mac becomes much more unrestrained, after I changed the rate to its maximum, compare to the default value (which I’ve long forgotten). You should try it and you will know what I mean.