Ninja
Shinobi, or ninja, are the primary focus of the Naruto series. They are usually found in ninja villages. The leader of one of the five most powerful ninja villages is called a Kage (''shadow''). The Kage can send shinobi of the village on missions and makes sure the village is okay. The Kage is also the person who gives orders to the village's ANBU.
Shinobi are given ranks based on their power and ability. The first rank, Genin, is gained by completing training at the Ninja Academy. After passing the Chunin exam, one can get the Chunin rank. The third rank is Jounin and the last is Kage.
A shinobi who has defected from their village is called a nuke-nin (missing ninja). Nuke-nin have a bounty placed on their heads by the Kage of the village and also, the village ANBU are sent to destroy their body.
Shinobi are known for their use of ninja techiques.
Chakra
Chakra is the moulding of physical and spiritual energy that is channelled through the body with the chakra circulatory system. Chakra is used to perform ninja techniques. Different ninja have different sized chakra reserves, therefore some people can use more chakra consuming techniques.
There are different types of chakra, such as sage chakra, which is created by the moulding of physical, spiritual and natural energy. To use sage chakra, the user needs to stay still to gather the natural energy.
Ninjutsu
Ninjutsu are techniques used by ninja. The user uses their chakra to perform feats that otherwise could not be possible. A way to perform ninja techniques is to use handseals. There are two ways to manipulate chakra to use ninjutsu, shape transformation controls the form of chakra and nature transformation gives the chakra an elemental nature.
Ninja Tools
Ninja tools are tools used by ninja. A ninja tool could be a weapon like a sword. The most common ninja tools are kunai knives and shuriken (ninja stars). A nina tool could also be any additional item commonly used by ninja, such as scrolls, forehead protectors, flak jackets and weapon pouches. A ninja tool might even be a living thing, such as the Inuzuka clan's ninken.