erms STD and STI, why the medical community prefers one over the other, and how AFC Chattanooga can help with testing and treatment. Schedule a visit online today. Is There a Difference Between an STD and an STI? While the terms STD and STI are often used interchangeably, they have distinct meanings in a medical context. Both terms refer to infections that are primarily transmitted through sexual contact, caused by viruses, bacteria, or parasites. Common ...