The word mustafid evokes the idea of spreading or overflowing. In reporting terminology, it can describe a narration distributed by several routes. A group of jurists treats mashhur and mustafid as two names for the same general kind of report.
«وَهُوَ الْمُسْتَفِيضُ عَلَى رَأْيِ جَمَاعَةٍ مِنْ أَئِمَّةِ الْفُقَهَاءِ»
According to a group of leading jurists, this is also called mustafid.
When an author uses the terms interchangeably, both indicate a report spread through several routes without attaining tawatur. Such synonymy should not be imposed upon every scholar’s terminology or upon other disciplines.