Retention time is how long a component takes to travel through the chromatographic system under a given method. Under fixed conditions it is reproducible, so it can be compared against a reference standard run on the same system.
It is not an identity test on its own: unrelated molecules can share a retention time, and the same molecule elutes at a different time on a different column or gradient. Identity is confirmed by mass spectrometry.
See also
For in vitro laboratory research only. Not for human or veterinary use. This library describes chemistry, analytical methods and published laboratory research; it gives no guidance on use in people or animals.