Sexually transmitted diseases are illnesses that can be transmitted between humans through sexual contact. This includes AIDS, which is caused by the HIV virus and progressively weakens the immune system if untreated. Gonorrhea is another common STD caused by bacteria that infects warm, moist areas and often has few or no symptoms. While treatable with antibiotics, untreated STDs can lead to long-term health issues like infertility. Prevention involves proper condom use, testing, treatment if infected, and education to promote safe sexual practices.