A sexually transmitted disease (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 human immunodeficiency virus (HIV). Many STDs can be asymptomatic, meaning individuals may not show symptoms but can still transmit the infection to others. Prevention of STDs can be achieved through safe sex practices, such as using condoms and having regular health check-ups. Early detection and treatment are crucial, as untreated STDs can lead to serious health complications, including infertility and increased risk of HIV transmission.