What falls under ASD?

Could you please clarify for me what specific entities or phenomena are typically encompassed within the term "ASD"? I'm particularly interested in understanding the context in which this acronym is commonly used, as well as any key characteristics or attributes that define what falls under its purview. Is it a legal, medical, or technological term? And if possible, could you provide a concise list or examples of what is generally considered to be within the scope of ASD?