For a while, I meet the word "marginal" in a lot of texts on economics and/or math, but I have difficulty to understand it intuitively.

Margin is some sort of a limit, a border, over which something doesn't usually go.

Why then the unconditional probability is also called the marginal probability? What does margin have to do with the unconditionality?

I have just read a phrase in a math stats book: unconditional probability (aka marginal probability) refers to the probability of an event regardless of the past or future occurrence of other events.

Thank you very much.