Sasine is like a special way of saying "this person officially owns this piece of land or property."
It’s like when you play a game with your friends and you say "this is my toy," and everyone knows that it’s really yours. Except that with sasine, it’s a very serious and official way to say that someone owns a piece of land or property.
When someone buys a piece of land, they need to make sure that they become the official owner, so nobody else can say that it’s theirs. To do that, they need to have something called sasine.
Now, imagine a big book where everyone’s name is written down, and the book is kept in a really special place. When someone buys land, they need to go to this special place and write their name in the book next to the land that they bought. This is called "registering the sasine."
After they do this, everyone who checks the book will know that this person officially owns that piece of land or property.
So, sasine is basically a way to make sure that everyone knows who really owns a piece of land or property, and it keeps people from arguing or fighting over who gets to use or live on the land.