The terahertz electromagnetic band has been foreseen as a promising candidate to accommodate the everincreasing wireless data traffic. To this end, the development of novel transceiver architectures and signal processing solutions is crucial to handling massive data volume transmitted over terahertz wireless communications networks. In this paper, we propose a waveform that shows full compliance with the spectral emission mask imposed by the IEEE Standard for terahertz communications. The designed waveform exploits 99.3% of the total in-band energy admissible by this mask and provides an extra degree of freedom for out-of-band interference management. A proof-of-concept experiment is conducted using a 300 GHz photonics-based terahertz communications link to demonstrate the generation and wireless transmission of the proposed waveform. Experimentally validated bit error rates show that the proposed waveform outperforms the widely adopted raisedcosine waveform and the better-than-Nyquist waveform even when the Nyquist criterion for inter-symbol interference-free signaling is not satisfied. Moreover, an error-free transmission at 1.44 Gbit/s is achieved without employing complicated digital signal processing at the receiver side.