-
Is it index or indexes?
The word index is singular. One index.
If you have more than one, you can form the plural according to Latin conventions:
indices
or according to English conventions:
indexes.
Preference varies...
-
What is an index?
An index is in the back of a book that tells you what page number you will find a certain thing you are looking for.
-
What is the index?
in a book there is a section that tells you where things are.
-
What is in an index?
the back of a book