A sexually transmitted disease, or STD, is an infection that is primarily spread through sexual contact. This includes vaginal, anal, and oral sex. Common STDs include chlamydia, gonorrhea, syphilis, and HIV. Many STDs can be asymptomatic, meaning individuals may not show symptoms but can still transmit the infection to others. Preventing STDs involves practicing safe sex, such as using condoms and getting regular health check-ups. Vaccines are available for certain STDs, like human papillomavirus (HPV) and hepatitis B. Early detection and treatment are crucial for managing STDs and reducing the risk of complications.