The defect live range is a measure of the length of development time between when a defect is injected into the product and the development time at which the defect is detetcted and removed.

For example, an interface specification in the architecture contains a datatype for a parameter in a method that is too restrictive. At system test time, a test case is derived from the requirements and that results in a value outside  of the datatype of the parameter. The defect is detected by the test. The defect live range is architecture to system test.