1. Shell Language: One major difference between Fish Shell and iTerm2 is the shell language they use. Fish Shell utilizes its own scripting language, which is designed to be more intuitive and provide helpful suggestions as you type commands. On the other hand, iTerm2 supports various shell languages such as Bash, Zsh, and Fish, allowing users to choose their preferred scripting language.

2. Auto-Completion: Fish Shell is known for its powerful auto-completion feature. It not only completes commands but also suggests options, file paths, and relevant flags. Moreover, Fish Shell's auto-completion works dynamically by analyzing the available data, making it highly efficient and accurate. While iTerm2 also offers auto-completion, it relies on the underlying shell language's capabilities and may not be as extensive as Fish Shell's auto-completion.

3. Customization: When it comes to customization, iTerm2 provides a wide range of options to personalize the terminal appearance and behavior. Users can change colors, fonts, and even create multiple profiles with different settings. Additionally, iTerm2 supports extensive configuration through preferences, making it easier to tailor the terminal to individual preferences. In contrast, Fish Shell has limited customization options and focuses more on providing a user-friendly default configuration.

4. Shell Prompt: The shell prompt, which displays information and allows for command input, is another differentiating factor between Fish Shell and iTerm2. Fish Shell has a default prompt that includes relevant information, such as the current directory and Git branch status. It also uses colors and icons to enhance visual representation. On the other hand, iTerm2 does not have its own default prompt and relies on the shell language's prompt customization options.

5. Syntax Highlighting: Fish Shell excels in syntax highlighting, making it easier to read and understand commands. It colorizes different parts of a command to distinguish between commands, arguments, variables, and options. This visual aid improves readability and helps prevent syntax errors. While iTerm2 supports basic syntax highlighting, its capabilities may be limited compared to Fish Shell.

6. Plugin Ecosystem: Fish Shell has an active and growing plugin ecosystem that allows users to extend its functionality further. These plugins can enhance auto-completion, add new commands, or integrate with other tools. iTerm2, on the other hand, does not have its own plugin system, but it can leverage plugins available for the supported shell languages.

In Summary, Fish Shell stands out with its intuitive scripting language, dynamic auto-completion, and strong focus on user-friendliness, while iTerm2 offers extensive customization options, support for multiple shell languages, and a versatile terminal emulator. The choice between the two depends on individual preferences and requirements.