I have looked this up but the definitions for the both seem to be the same. Verbose and Single User modes are like superusers. But what exactly is the difference between the two?
Verbose boot is nothing like "superuser". Verbose just means it'll giver "verbose" output when booting; I.e. print every step of the booting process to the screen. It's like turning on normally except with extra log messages. Single user mode boots only partially, then gives you a command prompt as soon as the system is ready to spawn a prompt, but before it's ready to facilitate full macOS, so you can poke around in things that you can't poke around with in a fully running system. Very rarely needed, but helpful to have as an option; Most the time just using sudo in a Terminal will give you enough "super user" access though