STI, or Sexually Transmitted Infection, refers to infections that are primarily spread through sexual contact. Common examples include chlamydia, gonorrhea, and syphilis. These infections can affect anyone who is sexually active, regardless of gender or sexual orientation. Many STIs can be asymptomatic, meaning individuals may not show symptoms but can still transmit the infection. Regular testing and safe practices, such as using condoms, are essential for prevention and early detection. If left untreated, some STIs can lead to serious health complications, including infertility and increased risk of HIV.