This question does not provide any information or context to determine what exactly is being referred to by the term "_______". However, we can approach this question by considering the given options and trying to make an inference based on common knowledge.

Option 'A': "-"

The hyphen "-" is commonly used as a punctuation mark to indicate a range or a pause in a sentence. However, in this context, it does not provide any meaningful information or clue to answer the question.

Option 'B':

In this case, leaving the option blank suggests that there is no specific answer or information provided. However, without any context, it is difficult to determine if this is the correct answer.

Option 'C':

Similar to option 'B', leaving the option blank implies that no information or answer is given. Without any further context, it is difficult to determine if this is the correct answer.

Option 'D':

This is the correct answer given in the question. However, since no context is provided, it is impossible to explain why option 'D' is correct or what it represents.

In conclusion, without any additional information or context, it is difficult to determine the correct answer for this question. The options provided do not give any meaningful clues to infer the answer. Therefore, it is important to consider the context and content provided in the question to arrive at a correct answer.