In the Context of Diagnostic Tests,what Does "Prevalence" Refer To

In the context of diagnostic tests,what does "prevalence" refer to?

A) The ability of a diagnostic test to detect only the medical condition in question
B) The ability of a diagnostic test to detect the medical condition in question in every patient who has the condition
C) The frequency of the condition in the population tested at a given time
D) The quantity that tells the probability that a result from a diagnostic test is correct