Platform 9 3/4

Platform 9 3/4 is a magical platform at King's Cross that in the Harry Potter continuum is where students gather on September 1st to board the Hogwarts Express to travel to Hogwarts, and then return to when leaving during the Christmas holidays or at the end of the term.

In fanfiction
In fanfics this often is the place where the new student is introduced to Harry and his friends, or any other character the Suethor fancies.