"Welcome to another year at Hogwarts! Before we begin I’d like to inform you all about some very important changes that’ll take effect immediately for the remainder of this school year. I am sure that you’ve seen that the House tables are, in fact, regular tables… for now. You see, Hogwarts will host the Inter-House Tournament. The Houses will be divided into two teams, and as a team–as a new House, rather–teamwork is essential in order to win."
Albus Dumbledore explaining the Inter-House Tournament.
The Inter-House Tournament is a tournament that was held for the first time at Hogwarts in 1994. It has been created by Albus Dumbledore for the sole purpose of making the individual Houses closer to each other, instead of seeing each other as rivals, and to forge friendship between all four Houses instead of just the House the students are in themselves.

The four Houses will be split into two teams, the Headmaster of Hogwarts gets to decide what those teams are. In 1994, Hufflepuff and Slytherin got to be Slytherpuff House and Gryffindor and Ravenclaw became known as Gryffinclaw.

During the tournament, the common rooms of the two Houses that got put into a team were made accessible to students from both Houses. In order to promote the Inter-House aspect of the game, changes were made to all of the dorms as well. The Heads of Houses that decided in which dorm all of their students get to sleep in when they first arrived as a first year, now had to make changes and mix their students together.