After writing this answer, I realized you might be describing a book with superscripts to coordinate text with secondary literature. If so, see Addendum.
What kind of book are you looking at? Another answer thoroughly explained footnotes and endnotes, plus other oddities. I can think of one or two other usages of superscripts. If you’re reading a classical book such as the Bible that exists in the English language in many official translations there may be numbers above many words that have been translated variously in various translations. This will be explained in the Forward, Introduction, Acknowledgements, or some other Editor’s/Author’s Notes before or after the main body of the book.
I have seen this in other books than the Bible but I can’t think at the moment what they were. Also, there should be a corresponding section somewhere to go with the numbers though this section can be easy to miss if a person does not read every single word between the two covers of the book. I mean every. single. word. This includes prefaces and publishing information. And I do not mean skim, I mean read to absorb and comprehend the meaning and implication of. I have had a lifelong habit of doing it but I’m weird that way.
Just now I found a way to illustrate. Below are photographs taken of pages in my HarperCollins Study Bible New Revised Standard Version, A New Annotated Edition by the Society of Biblical Literature, 1993, used while I was in Seminary. Image 1 is of the set of pages for Matt. 11: 18-Matt. 12:25. As you will note, Image 2 zooms in on the top left corner of this set of pages in order to work with Matt. 11:18-Matt. 12:3. More below.
If you look at Image 1, you will note that the body of the text on both pages is divided into two main sections:
- the biblical text, which constitutes the Bible that is being studied.
- the study notes that compare various parts (verses, in this case) and otherwise comment on the biblical text on those two pages.
I circled those two main sections; the biblical text is circled in lime or light green and the study notes are circled in orange. But there’s a third section, much smaller and very easy to miss if it’s not colour-coded. It’s the tiny section at the lower-right corner of the biblical text circled in yellow and bluish-green or cyan. In this Study Bible, that is your corresponding section that goes with the superscripts in the text on that page. More under Image 2.
I found and circled three superscript symbols in this text: s, t, and u. I also circled each corresponding symbol in the section at the bottom right corner of the biblical text. This is an example of the translators providing the reader with the alternative words used by other translators. To quote Matt. 11:19 in the NRSV above:
Yet wisdom is vindicated by her deeds.
There is a superscript ‘s’ following the word “deeds.” If we look up the superscript ‘s’ in the key at the bottom, we see:
Other ancient authorities read ‘children’.
Now we know that the ancient word in the original language is variously translated, sometimes “deeds,” sometimes “children.” If we wish to further research this to understand the reason, that is up to us.
If we look at the word marked with subscript ‘t’ we see that the original word can be translated as either “thank” or “praise,” a difference that is not quite as troubling as that between “deeds” and “children.”
As for subscript ‘u’, I would argue there is no difference in meaning at all but apparently the translators considered it important to make a note of it. They rendered the original:
for such was your gracious will
They note that it might also be rendered:
for so it was well-pleasing in your sight
To answer this question, since you don’t indicate at all what kind of book you are referring to, I cannot help you specifically. But in this answer I show how superscripts are sometimes used in classical texts translated into English from other languages to mark words or parts of the text that is variously translated by various legitimate/official translators. This does not include translators like you or me who might happen to know Ancient Hebrew and undertake to translate a passage for discussion on Quora or on our blog.
Superscripts may also appear in classical texts such as Shakespeare that were originally written in English. This is especially the case when a text is published specifically for use with secondary literature. Secondary literature is essays, papers, journal articles, and books that have been written on the classical text. I’m not sure if I have an example on hard to illustrate. However, such a book might not include a key like the cyan and yellow circled section in Image 1 above.
However, there should be an indicator what system is used to coordinate the text with secondary literature. This is most likely inserted as a line of text somewhere in the preface or in the notes of the author or editor or in the publishing info and if one is not familiar with the topic of that specific book and scholarly discussions around it, one might not recognize the terms. I think that fits the situation you describe.