Failures are observed only if they occur prior to a particular time. A unit surviving past that time is considered a right-censored observation. Right-censored data are sometimes time-censored or failure-censored. Time censoring means that you run the study for a specified period of time. All units still running at the end time are time censored. This is also known as Type I censoring on the right. Failure censoring means that you run the study until you observe a specified number of failures. This is known as Type II censoring on the right.