# 2.3 - What is Probability (Informally)?

2.3 - What is Probability (Informally)?We'll get to the more formal definition of probability soon, but let's think about probability just informally for a moment. How about this as an informal definition?

- Probability
- a number between 0 and 1
- a number closer to 0 means "not likely"
- a number closer to 1 means "quite likely"
- If the probability of an event is exactly 0, then the event can't occur. If the probability of an event is exactly 1, then the event will definitely occur.

## Try It!

Can you think of an event that cannot occur? Can you think of an event that will definitely occur?

An example of an event that canâ€™t occur is rolling a seven from a fair six-sided die with face values {1, 2, 3, 4, 5, 6}. An example of an event that will definitely occur is the sun setting tonight.