Fibers are classified into single-mode (SM) and multi-mode (MM) fibers based on the number of supported transmission modes. A fiber that has a core diameter greatly exceeding optical wavelengths and permits tens and even hundreds of transmission modes is called MM fiber. Typically, this fiber includes a small light-carrying core of about 9µm diameter. This allows the cables to transmit data over much longer distances than multimode fibers, with less signal loss and better quality. Let's break down these terms in simple, clear language with practical examples.