What does YoE actually mean?

Job postings will ask for certain years of experience (YoE). Common values are 3 years, 5 years, 7 years, 10 years, and 15 years.

What skills should people at these YoE levels have?

Is it possible to "level up"?

For example, could someone with 3 YoE quickly learn enough to become someone with 5 YoE? Could someone with 5 YoE quickly learn enough to become someone with 10 YoE?

At what point would YoE not matter anymore? For example, would there be a difference between someone with 20 YoE and 25 YoE?