The odds are the chances that something will happen. If you flip a coin, the odds are 50-50 you'll get heads.
When we talk about odds, we're talking about probabilities, specifically, how likely it is that something will happen. Is there a 5% chance? Is there a 95% chance? If there's a 95% chance, then the odds are great. We can talk about the odds of anything happening, as long as it hasn't happened yet. Anyone predicting the weather is telling the odds of rain or snow — they don't know for sure. If something strange happens people often say, "What were the odds of that?", which means: "I can't believe that happened. The odds were against it."