Excess is too much of something, like big-time overindulgence. Eating to excess makes your stomach hurt, and spending to excess means you can't pay your credit card bills.
Excess comes from the Latin word excessus meaning, "go out, going beyond the bounds of reason," like eating and spending in excess. (Not so reasonable.) Although it spends most of its time as a noun, it can also be an adjective to describe "more than is required or needed," like when excess water spills over the top of the bathtub, or those excess pounds spill over the top of your jeans.