What is a "defense" in the context of criminal law?

In criminal law, a "defense" refers to a legal argument presented by a defendant aimed at challenging the prosecution's case. It is the mechanism through which the defendant seeks to create reasonable doubt about their guilt or to justify their actions legally. This can include various strategies such as presenting evidence, witnesses, or expert opinions that contradict the prosecution's claims, asserting that the defendant was not at the crime scene, or even claiming that their actions were justified under certain circumstances (like self-defense).

The reasons behind the other choices not being correct further clarify the importance of understanding what constitutes a defense. A strategy to enhance the prosecution's case would imply actions taken by the defense that support the prosecutor's arguments, which contradicts the essence of what a defense does. A plea for leniency based on personal circumstances tends to fall under sentencing considerations rather than functioning as a defense against the charges themselves. The expectation for the defendant to testify is often a strategic choice rather than a requirement of presenting a defense; defendants can choose whether or not to take the stand. Thus, the core function of a defense is to counteract the prosecution's evidence and allegations, making option B the correct choice.