What Is a Terminal Emulator?

I use iTerm2 frequently for VPS and local CLI tasks. When trying to explain it to a designer, I realized my concepts were fuzzy. The iTerm2 site says: “iTerm2 is a terminal emulator for macOS that does amazing things.” What does that mean?

Terminal vs. Shell vs. Terminal Emulator — here’s a quick summary:

1. Terminal: hardware or software used to access a computer. Physical terminals (keyboard/monitor) vs. virtual terminals (apps on another machine). iTerm2 is a virtual terminal — a terminal emulator.
2. Shell: the program providing the command interface (bash/zsh/fish). Shells are interpreters and languages.
3. Terminal emulator: software that emulates a terminal, hosting a shell and rendering its I/O.

Recently I’ve been building a Web “shell” (really a web terminal) to access servers via the browser. Strictly speaking, it’s a terminal UI in the web that hosts a shell on the server — but colloquially, “web shell” sticks.