Check in between filter helps you to find all reservations that have at least one item that starts between this two dates. Check out filter finds all reservations that have at least one last item with end date between this two dates. Reservation period between is filter that helps you to find reservations with travel dates between some specific period..For example, if reservation has one item with travel dates from 3/11 till 10/11 then I will find it by filter Check in only if I include first date. Reservation period between filter will find this reservation by any dates that include travel dates, even if I don’t include check in and check out dates.