In-ear monitors (IEMs) and in-ear headphones are similar in form but used for different purposes. IEMs are designed for musicians on stage, while in-ear headphones are used for personal listening.

    IEMs aim to provide a clear and accurate representation of the audio, allowing the musician to hear themselves and the other band members in a similar way to what the audience is hearing. They also provide better isolation, meaning the musician can hear more clearly even in a loud stage environment. Additionally, they are more comfortable to wear and sit stably in the ear canal.

    In-ear headphones are popular among people who want to listen to music on the go, such as during commuting, running, or at the gym. They are designed for people to enjoy music in a personal way. They may have distinctive sound signatures that are tailored to specific music genres. Accurate sound reproduction is not a must need.

    Nowadays, the two are heavily overlapped. One may use IEMs for personal musical enjoyment. And many high-fidelity in-ear headphones positioned themselves as having the most accurate sound.
    The boundaries have blurred, and one shall choose the product based on the actual offering, not what the name suggests.