To be precise, it is the script book for the stage play, Harry Potter and the Cursed Child. And it’s set to be released sometime this summer. According to Pottermore:
Readers and moviegoers last saw Harry waving off his children at Platform Nine and Three-Quarters, 19 years after the Battle of Hogwarts, in the epilogue to Harry Potter and the Deathly Hallows. Harry Potter and the Cursed Child picks up after that moment and is staged in two parts, due to the ‘epic nature of the story’.
I’m assuming a “script book” is the script of the play bound in book form. If that’s not correct, I’d appreciate someone enlightening me.