Back pay refers to salary or wages owed to an employee for work already performed. Other synonyms for back pay include retroactive pay, wage arrears, and past-due salary. In legal terms, back pay may also be described as unpaid earnings or back wages. The concept of back pay is typically used in labor and employment law to provide a remedy to employees who have been underpaid or not paid at all for work they have done. Employers who fail to provide back pay may be held liable for damages and may be required to pay fines or penalties.