Imagine you have a bunch of toys in a box. You can group these toys into piles of a certain size. For example, if you group the toys into piles of three, you will have leftovers if the number of toys is not evenly divisible by three. The leftover toys represent what we call the "remainder".
In math, we use a special symbol called the "%" (modulus) operator to represent the remainder. For example, if we write "5%2", it means we want to know the remainder when we divide 5 by 2. In this case, the answer is 1, because when we divide 5 by 2, we get 2 with a remainder of 1.
Now, let's take this idea even further. Instead of just looking at remainders, let's look at the entire groups that we formed earlier. In math, we call these groups "modules". We write it using the symbol "mod". For example, if we write "5 mod 2", it means we want to group 5 into piles of 2 and see how many complete piles we get. In this case, the answer is 2, because we can group 5 into piles of 2, and we will have 2 complete piles and a remainder of 1.
The concept of modules is often used in math to solve problems involving circular or repeating patterns. For example, if we are trying to find out what day of the week it will be in 100 days, we can use the concept of modules. There are 7 days in a week, so we can write 100 mod 7 to find out how many full weeks there are and how many days are left over. In this case, the answer is 2, so if today is Tuesday, in 100 days it will be Thursday.