A "gap" is the space between two things. For example, some people have "gaps" between their teeth.
You can also use the word "gap" to talk about numbers or experiences that are very different from each other.
The pay gap between men and women is getting smaller, but it's still a serious issue.
There's a huge gap between how I grew up as the son of a poor farmer and how most of my classmates were raised.
Usually when someone talks about the "gap between" things it suggests that those things should be closer. For example, you can talk about the "gap" between:
- men and women
- politicians and citizens
- your financial reality and your wishes
- how much executives are paid in a company vs. regular employees