This "Gold Standard" is the most accurate type of test accepted in every country.
RT-PCR (or PCR) tests are the most accurate tests available for detecting whether a person has a Covid-19 infection or not. Sensitivity is the ability to detect the disease so high sensitivity gives confidence that there are not many false negatives. It gives confidence that the negatives do not have the disease.High Specificity rules out those that do not have the disease and so does not produce many false positives. It gives confidence that a positive test does have the disease.
These tests are widely approved for travel and is the de facto standard for Covid-19 testing. Although you should consult government websites and trusted public health information for your destination and transit points of your journey if you are travelling.