Statistics: what it is or what are they (i.e., it is singular or plural)?

The word "statistics" is used as both a singular and as a plural.

The word "statistics" is used as the plural of "statistic". From Wikipedia: "A statistic (singular) is a single measure of some attribute of a sample." So if you have two or more of these, you would say something like "the statistics are available".

As a singular word, "statistics" refers to a field of study. We have (also from Wikipedia): "Statistics is the study of the collection, analysis, interpretation, presentation, and organization of data."

Note the singular in this meaning "Statistics is".

If you were asking about the nature of the field of study, it would be correct to ask, "What is statistics?"

If you were unclear about the use of the words "statistic" and "parameter", you could ask, "What are statistics and how are they different from parameters?"