Jak'tahla was a Klingon word that roughly translated into the Klingon version of puberty that affected Klingons during their teenage years. It was characterized by accelerated hair growth, mood swings, increased aggressive tendencies, the appearance of gorches on the Klingon's face, among other things.
Jean-Luc Picard quipped that the translation of puberty "hardly does it justice". (Star Trek: Insurrection)
In 2375, the metaphasic radiation from the Ba'ku's ring's caused Lieutenant Commander Worf to re-enter jak'tahla. (Star Trek: Insurrection)