"Bells and whistles" is an idiomatic expression that refers to the additional, often elaborate or decorative features or components of a product, system, or project that are not strictly necessary for its basic functionality but are added to enhance its attractiveness, appeal, or perceived value. These extra features are often designed to impress or delight users, but they may not significantly contribute to the core purpose or functionality of the item.
For example:
Imagine purchasing a high-end smartphone. While the essential functions of calling, texting, and browsing are its core features, the phone might also come with "bells and whistles" such as a built-in virtual assistant, fancy animated wallpapers, advanced camera filters, or gesture controls. These extras might not be essential for basic phone usage, but they contribute to the phone's overall user experience.

Similarly, in software development, "bells and whistles" might refer to extra features or graphical enhancements in an application that don't directly impact its main functionality. A word processing software could have basic text editing as its core function, but it might include elaborate font options, clip art libraries, and intricate formatting tools as "bells and whistles."

In summary, "bells and whistles" encapsulate non-essential but appealing features that can enhance the overall experience or aesthetic of a product, often with the intention of making it stand out from simpler or more basic alternatives.