Definitions
from The American Heritage® Dictionary of the English Language, 4th Edition
 n. A fraction or ratio with 100 understood as the denominator; for example, 0.98 equals a percentage of 98.
 n. The result obtained by multiplying a quantity by a percent.
 n. A proportion or share in relation to a whole; a part: The hecklers constituted only a small percentage of the audience.
 n. An amount, such as an allowance, duty, or commission, that varies in proportion to a larger sum, such as total sales: work for a percentage.
 n. Informal Advantage; gain: There is no percentage in work without pay.
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. The amount, number or rate of something, regarded as part of a total of 100; a part of a whole.
 n. A share of the profits.
 n. Benefit or advantage.
from the GNU version of the Collaborative International Dictionary of English
 n. A certain rate per cent; the allowance, duty, rate of interest, discount, or commission, on a hundred.
from The Century Dictionary and Cyclopedia
 n. Rate or proportion per hundred: as, the percentage of loss; the percentage of oxygen in some compound, or of pure metal in an ore; specifically, in com., an allowance, duty, commission, or rate of interest on a hundred; loosely, proportion in general.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
 n. a proportion in relation to a whole (which is usually the amount per hundred)
 n. assets belonging to or due to or contributed by an individual person or group
Etymologies
from Wiktionary, Creative Commons Attribution/ShareAlike License
Examples

Ma's trust index fell 1.7 percentage points from last month to 37.1 percent, against his distrust index of 44.7 percent  down 2.4 percentage points.

For every given level of your output a certain percentage is direct and indirect energy costs.
Coyote Blog » Blog Archive » I Am Tired of Hearing About Liquidity Traps

If a certain percentage is not normal then you are not removing enough of them and patients might die from missed diseased cases.
The Volokh Conspiracy » Is the Sixth Now the “Most Reversed” Circuit?

Though I still think assigning a percentage is a meaningless estimate.
My Favorite Economic Indicator, Arnold Kling  EconLog  Library of Economics and Liberty

This percentage is the highest rate in the 51 years that these estimates have been released.
Rabbi Steve Gutow: 43 Million Reasons for Congress to Get Serious

Some regions with "higher" gas prices still only spend 2% of their median income on gas, while the percentage is as high as 16% in Wilcox County, Alabama.
Gas Price Impact Map: Rural US Getting Slammed By $4 Gas  The Consumerist

I think since the percentage is the same amoung the whites and the blacks.

I think the percentage is about half of what he gets – 23.5%.

Pondering the answer made me dig: the Joshua Project references a Christianity Today article which briefly suggests the percentage is a low 2%.

I wish the poll would tell you how many people have voted so I could tell whether the percentage is a big deal or not.
EXTRALIFE – By Scott Johnson  The poll seems to be hootched
chained_bear commented on the word percentage
I'm kind of amazed this word hasn't yet been added. Today is November 20, 2008. (For Wordieternity.)
November 20, 2008