Final answer:
Abstinence is the decision and practice of refraining from sexual activity, and it is the only completely effective way to prevent the spread of sexually transmitted infections (STIs).
Step-by-step explanation:
The decision and practice of refraining from sexual activity is called abstinence. Abstinence is the only completely effective way to prevent the spread of sexually transmitted infections (STIs), including HIV. While safe sex practices such as condom use can reduce the risk of transmission, abstinence is the only way to be absolutely sure of not getting an STI.