The term "back tax" refers to the tax amount that is due and unpaid for a previous year. Synonyms for this term include "delinquent taxes," "unpaid taxes," "tax arrears," or simply "owed taxes." Other terms that might be used to describe someone who has not paid their taxes on time include "tax evader," "tax dodger," or "tax delinquent." It is important to note that failure to pay back taxes can result in heavy fines, penalties, or even legal action. Therefore, it is essential to keep track of one's tax obligations and pay them on time to avoid future problems with the Internal Revenue Service (IRS).