The International Centre for Settlement of Investment Disputes is a place where people and companies from different countries can go to settle disagreements and arguments about investments.
Let's say that you have a big toy store in the United States and you want to open a branch in Canada. You need to invest your money to buy toys, hire people and rent a store. However, when you get to Canada, you find out that the rules are different there and you have to pay more taxes than you expected. You are not happy with this and you want to sue the Canadian government to get your money back.
This is where the International Centre for Settlement of Investment Disputes (ICSID) comes in. They provide a safe and neutral place for you and the Canadian government to talk, and they help to find a fair and reasonable solution to the problem.
It's kind of like when you and your friend can't decide who gets to play with a toy first. Your mom or dad might step in and help you come up with a plan that makes both of you happy.
The ICSID is very important because it helps to keep international trade fair and peaceful by making sure that everyone follows the rules and there is no unfair advantage given to anyone.