See also: Trainer's Journey
“Trainer's Leave” is what the first instance of a youth's Trainer's Journey is called most of the time. Unlike subsequent Journeys, the first Journey, or Leave, tends to be arranged at a school-wide or city-wide level to take place when the children are still in school, sending all students out on their own adventures that count as an academic period (of eg.: one semester, or sometimes one year).
Being the first Journey, the Leave begins for most people with them becoming acquainted with who will become their starter Pokémon.