Magic Number Subnetting is a technique in IPv4 subnetting that simplifies the process by using "magic numbers." These numbers are powers of 2 and are used to determine subnet sizes and boundaries more easily. The magic number is calculated by dividing 256 (maximum value in an octet) by the required number of subnets. Subnet boundaries are then found by adding the magic number successively. This method streamlines the subnetting process, making it more straightforward, especially when dealing with powers of 2.