Median survival is defined as the time after which 50% of people with a particular condition are still living, and 50% have died. For example, a median survival of 6 months would indicate that after 6 months, 50% of people with that condition would be alive, and 50% would have passed away.
Median survival is also a term used in clinical trials, when a drug or treatment is being evaluated to see if it will extend life.
Jack was told that the median survival for people with stage 3B lung cancer is 13 months. This would mean that, statistically, he had about a 50% chance of being alive with his disease in 13 months.