Zsh is the shell which is a mini language and environment, so you can run that in many different terminals. OhMyZsh is a set of configuration scripts and plugin

Zsh is the shell which is a mini language and environment, so you can run that in many different terminals. OhMyZsh is a set of configuration scripts and plugins to configure Zsh. A terminal is the thing that renders text, handles input and all the escaping complexities. So it's usually the UI/colors around the text that the shell provides. Old terminals were even physical devices with ports that allowed connecting to headless computers.