Southwest Airlines flight 48 encountered turbulence during cruise. One flight attendant sustained serious injuries. The airplane was not damaged. The regularly scheduled passenger flight was operating under the provisions of 14 Code of Federal Regulations Part 121 from the Kansas City International Airport (MCI), Kansas City, Missouri, to the Denver International Airport (DEN), Denver, Colorado. According to the flight attendant, as she was pouring coffee into cups while in the front galley, the airplane encountered very light turbulence which she described as a ‘very light bump’. During the event, the coffee pot flipped over and spilled coffee onto the back of her hand, resulting in 2nd degree burns. After the event, the captain called back to the cabin to apologize for the turbulence and advised that it was unexpected. The flight attendant continued duties after the event, and there was no further turbulence. Prior to the flight, the captain discussed the possibility of turbulence during the preflight briefing, however the turbulence associated with the event was unannounced and unexpected.