This foundational document establishes international definitions and terminology for Software as a Medical Device (SaMD), distinguishing it from hardware-based medical devices. SaMD is defined as software intended for use in achieving a medical purpose without being part of a hardware medical device. This definition serves as the baseline reference for all subsequent IMDRF SaMD guidance documents and national regulatory frameworks. The FDA, PMDA, and EU MDR all reference this definition in their respective SaMD regulatory frameworks, making it essential to understanding harmonized international SaMD regulation and classification schemes adopted globally.