A tax advisor is a person who advises clients about tax laws and strategies.
For example, a tax advisor might help a client structure his assets such that his estate taxes are lower. A tax advisor might help a company organize itself so that its shareholders pay less in taxes or so that an acquisition does not generate a large tax liability. Tax advisors must obtain special training and education in order to provide information that complies with current tax laws.
Tax advisors are skilled professionals that should be extremely well-read in IRS guidelines and rules. They are not always CPAs or attorneys; in those cases, tax advisors must take a written examination or have previous IRS experience in order to register as an "enrolled agent" with the IRS. Treasury Department Circular Number 230 sets forth the requirements for who can practice before the IRS.