There are shinobi in the narrow sense of the word and in the wide sense of the word. In the narrow sense, only samurai men who went through complete shinobijutsu training were considered "true" shinobi. These would be samurai men from Iga and Koga as they had formal shinobijutsu schools. Along with spying, during the turbulent times of the Warring states they often performed their arts on the battlefield as well, through various acts of irregular warfare - sabotage, night attacks, ambushes, misdirection etc. In the wide sense of the word, anyone who performed any of the arts a shinobi would do and was employed for it was considered a shinobi. A well known example of a shinobi in the wide sense of the word is Fuuma Kotaro, he was never formally trained in Iga or Koga and the clan itself specialized in performing irregular warfare on behalf of the Hojo clan. Apparently they performed no, if any, espionage. Additionally, shinobi from Iga and Koga rarely operated alone and had a lot of helpers doing the wet work, that also included women who could be used to spy and eavesdrop by pretending to be maids and such.
