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...
There are 3 types. B-tree( good for a column with less than 240 unique values), Bitmap, function. The last two are used in Oracle 9i and above versions, so they are smarter. Prior versions uis B-tree...