The phrase "neither fish, flesh, nor good red herring" refers to something or someone that is difficult to classify or define. There are many synonyms for this phrase including "in-between," "ambiguous," "vague," "equivocal," "unclear," "indefinable," "indeterminate," "unclassifiable," and "nebulous." These words all suggest that something or someone cannot be easily categorized or defined. The phrase can be used to describe a wide range of things, from a work of art or a piece of music that defies categorization, to a person whose motives or personality are hard to understand. Ultimately, the phrase is a reminder that not everything can be neatly labeled or categorized.