The new phone is basically the same size as the old 5S but comes with updated internal components and features that were previously only available on the newer 6-series iPhones.
Gurman reported that the "se" is supposed to mean both the "special" and "enhanced" edition of the old 5S phone.
Despite the popularity of the iPhone 6 series, there has been some demand for a smaller version of the iPhone, like the 5S. Gurman says Apple is hoping the new 5se to cause those 5S users to upgrade their old phones.
According to Gurman, the 5se also comes with similar curved edges like the 6S or 6S plus, and features that include Live Photos and Apple Pay. It also comes with an 8 megapixel camera and the same color options as the 6S.