When President Trump meets Kim Jong-un, the first face-to-face encounter between leaders of the United States and North Korea after nearly seven decades of hostility, they will talk about denuclearization and maybe even a peace treaty.

What do those terms mean? Are they even defined the same way by everyone? Which one would happen first and why is the sequence important?

The mistrust between North Korea and the United States, mixed with the unpredictability of their current leaders, has made the diplomacy behind the summit meeting in Singapore on Tuesday especially complex.

“It’s pretty clear that there is a strong inclination by both leaders to have a good show, a good P.R. opportunity, and this is where it gets risky and dangerous,” Duyeon Kim, a senior research fellow at the Korean Peninsula Future Forum, told a panel discussion at the Heritage Foundation in Washington this past week. “My concern is that the two leaders — especially Trump — would want to declare peace, because it sounds good and it’s historic and unprecedented.”