Immigration reduction means that there are less people from other countries coming to live in a particular place. It's like when you have a big family and you don't want to have too many guests staying with you because there's not enough room in the house.
When a country wants to reduce immigration, they may make rules that make it harder for people from other countries to come and live there. For example, they might say that only people with certain skills or qualifications can move there, or they might ask them to have a certain amount of money before they come.
The reason why a country might want to reduce immigration is because they might feel like there are already too many people living there or they might worry that the new people coming in will take jobs away from people who already live there. It's like if you have a pizza and all your friends want a slice, but if you give too many slices away, you won't have any left for yourself.
Reducing immigration can be a controversial topic because some people believe that welcoming new people and different cultures is important, while others think that it might cause problems or change the way things are done. It's like if you have a really nice playroom and someone else comes in and wants to play with your toys - it can be fun, but it can also be difficult to share sometimes!