  Communication security has to evolve to a higher plane in the face of the
threat from the massive computing power of the emerging quantum computers.
Quantum secure direct communication (QSDC) constitutes a promising branch of
quantum communication, which is provably secure and overcomes the threat of
quantum computing, whilst conveying secret messages directly via the quantum
channel. In this survey, we highlight the motivation and the status of QSDC
research with special emphasis on its theoretical basis and experimental
verification. We will detail the associated point-to-point communication
protocols and show how information is protected and transmitted. Finally, we
discuss the open challenges as well as the future trends of QSDC networks,
emphasizing again that QSDC is not a pure quantum key distribution (QKD)
protocol, but a fully-fledged secure communication scheme.
