Credibility is simply the fact that someone can be trusted or believed.
Credibility can also be defined as
"the quality or power of inspiring belief". Credible sources, are therefore, reliable sources that provide information that one can believe to be true.
Because Joe probably used steroid to enhance his performance during weightlifting or maybe have seen what steroids do to people that use it during physical fitness and other physical activities, the informative speech he will give concerning the use if drugs in physical fitness will be credible. He will speak from his own personal experience, and with what he has seen others pass through as well. His speech will be very Credible because he will speak using illustrations everyone can safely call reliable.
