Imagine you have a bunch of numbers written down in a rectangle, like you're playing a game of Sudoku. That rectangle is called a matrix. Now, let's say you want to split that matrix into two parts - one part that is on top of a diagonal line that goes from the top left corner to the bottom right corner, and another part that is below that diagonal line.
The Crout matrix decomposition is a way to do that splitting in a special way. The top part of the matrix will have ones along the diagonal line, while the bottom part will have numbers that help you calculate the original matrix.
This might sound complicated, but it's like taking a cake that is already baked and cutting it into two parts - one part that is already finished and can be eaten, and another part that needs a little more work to become a complete cake. In the same way, the first part of the matrix that we split off using the Crout matrix decomposition doesn't need any more work and can be used right away. The second part needs some more steps, but we can use it to recreate the original matrix if we do those steps correctly.
So, the Crout matrix decomposition is just a special way of splitting a matrix into two parts, where one part is already finished and the other part can be used to recreate the original matrix with a little more work.