Kāma

Kāma is the marking which Boruto received from defeating Momoshiki Ōtsutsuki. Though it's unfamiliar to the population at large, Kara has knowledge on it and similar seals.

Usage
Unconsciously using it, Boruto was capable of absorbing ninjutsu, which resulted in him collapsing as it was his first time accessing its power. Three years later, he could activate it at will.

Trivia

 * Although the kanji itself would normally be translated as, the furigana indicate the reading . "Kāma" means "wish", "desire" or "longing" in Hindu literature, but in Japanese, it is also an uncommon way to write "karma".