Tenketsu (点穴, English TV: Chakra Points, Literally meaning: pressure point) are nodes from which chakra can be released. The human body has 361 tenketsu, each of which is located along the chakra pathway system. Most ninja, even experienced jōnin, are only able to release chakra from the tenketsu on their hands or feet in order to augment their physical strength. Members of the Hyūga clan are uniquely able to expel chakra from any or all of their tenketsu, and have created jutsu such as the Eight Trigrams Palms Revolving Heaven to specifically take advantage of that. Additionally, in the anime, Hinata Hyūga was able to emit chakra from all of her tenketsu to form a layer of protection against Guren's Crystal Release: Jade Crystal Prison Technique, which ultimately saved her.
Tenketsu are very small, too small for even the Sharingan to see. Only the Byakugan is able to see another person's tenketsu, enabling a Byakugan-user to attack the tenketsu directly in order to block them, disrupting the flow of chakra and preventing opponent from using chakra; the Gentle Fist style of combat is focused around doing this.