The Excalbian Campaign was a mission which had taken place in the past of a fictional future created for William T. Riker.
In 2367, while exploring a cavern on Alpha Onias III, Commander Riker was rendered unconscious by gases. While unconscious, neural scanners scanned Riker's brain. The scanners used elements of Riker's reality and constructed a holodeck simulation with those elements interspersed throughout, so that it felt real to him. What Riker wanted, the scanners made possible.
In one of these simulations, on stardate 57398, Captain Riker, the commanding officer of the USS Enterprise-D, was awarded a commendation for exceptional leadership by Admiral Brettner during this campaign. In 2383, this campaign was mentioned in Riker's service record that was on display in his quarters on the Enterprise-D. (TNG: "Future Imperfect", okudagram)