The tax adviser must advise his client (a company or other organisation) so that he is not only in order with his tax administration, but can also optimise his tax situation. His work can be very specific, in the context of a specific acquisition or merger, for example, but also more general in the context of recurring support for all the company's declarations to the tax administration.
The profession is not legally protected, but the title of (internally) certified tax advisor is. The title is associated with the Institute of Tax Advisers and Accountants (IBA, ICE, or ITAA in English).