Check-in means a guest arrives that day. Stay means a guest is partway through a trip. Checkout means a guest leaves. Turn means one guest leaves and another arrives on the same day.
They show which site the booking came from. A is Airbnb, V is VRBO, and B is Booking.com.
That day is shown as a Turn, with the checkout and the new check-in both visible. It is a same-day turnover, not a double booking.