What is Net pay?
Net pay, or take-home pay, is what remains after the employer subtracts all withholdings from gross pay: federal (and state/local) income tax, FICA, and any voluntary deductions such as retirement contributions or health insurance premiums.
Net pay is the figure that hits the employee's bank account. The gap between gross and net is why a $60,000 salary does not mean $60,000 in the bank.
In practice
From $4,200 gross, after $500 income tax, $321 FICA and a $250 health premium, the employee's net pay is $3,129.