Nezaru The kind of ninja that dealt with the stealthy jobs like daimyo assassination and did things like jump from roof to roof to escape.Name means "roof monkey"
Rappa This kind of shinobi would dress as the enemy, gain access to the enemy castle, and start killing or burning which would throw the soldiers into utter chaos and random killings would take place in order to try to kill the intruder. But the intruder would look like them, so like I said, utter chaos occured. During the mayhem, the true intruder would open the gates and the intruder's army would enter and easily take over the castle.
Kusa These shinobi were body guards that hid in grass...Simple enough...There name means "grass"...