STI stands for Sexually Transmitted Infection, which is an infection that can be transmitted during sexual contact. If used correctly condoms can prevent STIs from being passed from an infected person to their sexual partner. Condoms are the only method of contraception that also protect from STIs.
This website here has information about different types of STI.
If you are sexually active, it's a good idea to be tested for STI’s on a regular basis. For most people it is recommended that you get checked about once a year.
The Advice Service offers free STI testing. However, if you have recently had or are expecting to have unprotected sexual contact with a new partner, it is best to get tested as soon as possible. The easiest way to get tested is to go to a GUM (Genito Urinary Medicine) or Contraceptive or Sexual Health Clinic. It's also the best place to go if you are experiencing symptoms and want to get checked out.
Palatine Contraception and Sexual Health Services have several clinics around the city.