A tax deduction is a deduction that a taxpayer may take on their total income assessed, as long as said tax deduction falls within the legal guidelines set forth by the Internal Revenue Service. What can be considered a tax deduction is dependent on how you earn your living. For instance, if you are self-employed you may be eligible to receive a tax deduction for any mileage that you incurred with regard to your business. However, if you work for someone else, and work at a factory, you cannot claim the mileage you incur driving back and forth to work each day. Tax deductions are beneficial in that they lower the amount of your gross income which must pay taxes on.