It implies high-end functionality beyond the basic criteria for a smartphone, such as the ability to be more tailored to a specific user's needs.
A Superphone usually incorporates state of the art technology, innovations in hardware, and newer refined software.
For example, having the latest SoC chip made from OEMs such as Qualcomm or Intel.
A superphone could also imply a certain set of physical characteristics that is unique, unusual, innovative, and not regularly seen in smartphones; an example of this are the edge-to-edge "bezel-less" displays found in higher-end smartphones such as the Samsung Galaxy S8 or the Essential Phone.
The body is curved horizontally, making it less likely to break when bent, for example when one sits on the phone by accident.