The PLOB bound, named after the initials of its discoverers (Pirandola-Laurenza-Ottaviani-Banchi), is a fundamental theoretical limit in quantum communications. It defines the maximum capacity of direct quantum communication, such as Quantum Key Distribution (QKD), without quantum repeaters over a lossy channel, like an optical fibe​​​​r. This bound delineates the optimal rate at which secret keys can be exchanged between parties and is crucial for understanding the efficiency and security of quantum communication systems. The PLOB bound serves as a benchmark for evaluating quantum communication protocols, where surpassing it is a significant goal for advancing quantum communication technologie​​​​​​s.