The DVLA is a British government office. Learner dictionaries still describe it as the place that collects road tax from vehicle owners, runs driving tests, and issues driving licences. That is the sense you are meeting, and it is what older British materials will assume. Though actually, in today’s UK the DVLA still handles licences, vehicle registration, and vehicle tax, but driving tests are run by another office. Students in Taiwan will not deal with the DVLA unless they live in or visit Britain, or they meet it in British English exams and news. It is an official name, always the letters, said as four letters, not a word. The nearest idea at home is the motor-vehicle office that keeps car records and licences — but that Taiwan office is not called the DVLA.