The foundation of yout tax bill is your gross income (the total of every dollar you were paid in a given year).
"Above-the-Line" are deductions you take before you get to your itemized deductions. If you put some of your earnings into certain tools - like a health savings account or a 401(k) - that money will be not be taxed now (if ever). These deductions are all taken "Above-the-Line" before you determine your Adjusted Gross Income.
You should note that many of your "Above-the-Line" deductions may be provided by your employer, so pay close attention to these company benefits.
