Sometimes the phrase "open house" is used when the parents of many students come to the school to see what the children have been doing. These open houses usually occur on a school night, and the parents can walk through the classrooms. These are more for younger grades.
It's usually called an Open House. Parent-teacher conferences can occur at an open house but they usually imply one-on-one type meetings as opposed to all the parents gathering to see the children's work.