The whiteboard is where Gregory House writes out symptoms to be reviewed by his team. Only House is allowed without reservation to use the whiteboard, but as a joke he assigned Cameron to write on the whiteboard in his absence, and Foreman if they were both absent. He didn't think Chase was ready to write on the whiteboard.
The whiteboard has been used for other purposes. In House vs. God, Chase used the whiteboard to keep score between House and God.
In Failure to Communicate, House was at an airport and used a large wall as a whiteboard.
In No Reason, House was in the ICU without a whiteboard and used one of the glass walls as a substitute.
In Airborne, House was without his whiteboard, and substituted an aircraft movie screen while he tried to diagnose a sick patient.
In Last Resort, House uses the wall of Cuddy's office as a substitute whiteboard.
In Twenty Vicodin, House was in prison and used the bottom of Asofa's bunk bed as a whiteboard.