You have filed your returns but didn't have the money to paywhat was owed. You may think, "Oh well---I will catch up next year." Before youknow it you find yourself several years in arrears and suddenlythere is a notice from the IRS, stating that you owethree or four times the original amount.
It's truly amazing how fast tax penalties and interest add up. Nowyou have a choice, you can write a big fat check and pay the full amount,including interest and penalties. Or you can just keepignoring them while the penalties and interest keep pilingup.