What does the term "improbable" describe?

The term "improbable" specifically describes something that is not likely to be true or to occur. This term is often used to indicate that a particular outcome or situation has a low chance of happening based on available evidence or reasoning. The essence of "improbable" lies in its association with doubt or skepticism regarding the likelihood of something being accurate or feasible.

In contrast, the other options present concepts that oppose the meaning of "improbable." For instance, the idea of something likely to happen or something that is certain directly contradicts the uncertainty that "improbable" conveys. Similarly, the notion of frequency suggests a repetition or regular occurrence, which is at odds with the rarity implied by "improbable." Thus, the correct answer effectively reflects the definition of the term, clearly aligning with its established usage in the English language.