"adherence to moral and ethical principles;
soundness of moral character; honesty."
(Follow the link if you would like to read the entire definition on Dictionary.com.)
Integrity sometimes means turning down a job, because you don't agree with some of the standards and procedures. It sometimes means, not promoting work that you can't stand behind, either because of flaws in the product/service or because you don't know anything about it. When it comes down to it, sometimes you have to choose between money and integrity, friends and integrity, family and integrity, power and integrity, and prestige and integrity. The road to integrity is not always an easy one.