Juinjutsu

are a type of techniques used to bring someone under the control of the user. By applying a seal to the victim's body, the user brings the victim's abilities and actions under their control. With a simple secret hand seal, the user can inflict great mental and physical torment on the victim. The exact workings of juinjutsu are kept secret.

Juinjutsu requires a great deal of skills to use, and suppressing one is equally difficult. Removal of the seal is nigh-impossible, as many opt to seal them away instead. The only known certain ways to remove a cursed seal is if either the applier or receiver dies, as with the Cursed Tongue Eradication Seal and Hyūga Main Family's Juinjutsu, respectively.

Trivia

 * The markings around Shukaku's body are naturally a cursed seal, allowing it to seal its opponents.
 * The marking of the Flying Thunder God Technique is likened to a cursed seal, as any victim marked by it is essentially sentenced to death.
 * In the anime, Victor applied a cursed seal onto himself to extend his own life. However, the seal was also eroding his health, which was compounded by his prolonged usage of his regenerative ability.