A telomere is a "genetic clock" in DNA. Every time a cell divides, the telomere grows shorter, allowing a person's age to be determined at the time the cell sample was taken.
In 2154, DoctorPhlox studied a cell sample of T'Pau that was being used to implicate her in a bombing of the United Earth Embassy. By examining the telomeres, Phlox found that the DNA on the bomb had been taken from T'Pau when she was an infant, and that she was therefore not responsible for the bombing. (ENT: "The Forge")
According to the text commentary on the Star Trek: Enterprise season 4 DVD set, the computer graphic displaying T'Pau's telomeres was a mistake. A special computer graphic was prepared, but a last-minute mix-up resulted in a generic display featuring bacteria, which can be seen on computer screens in sickbay throughout the run of Star Trek: Enterprise.