Literal: neither so much nor so bald; a literal juxtaposition suggesting moderation between two extremes.
2.
SpainLatin Americainformalcolloquial
Figurative: used to advise moderation or to reject exaggerated positions; 'not that extreme nor that negligible', meaning the truth lies somewhere in between or do not overstate things.
Examples:
ES: Oye, perdona, ni tanto ni tan calvo, alguien normal, de mi edad.