What does it mean to “defy the odds?” It's often used to describe an accomplishment of something that is seemingly improbable, or succeeding in something where people thought you would fail. Defying the odds means that the odds are stacked against you, and it's not very likely you'll make it.

What does it mean to even the odds?

In betting parlance to 'even the odds' is to make the odds closer to 'evens' - specifically to make unlikely events more likely. If the odds were ten to one against, if you make them five to one against you are 'evening the odds'. By extension 'evening the odds' is making an unlikely win (or other success) more likely.

What does decrease the odds mean?

To shorten the odds on something happening means to make it more likely to happen.