What is the difference between these types of documents?

I am applying to serveral undergraduate research programs this summer. Each of them ask for certain documents including:

CV

personal statement

statement of interest

cover form

cover letter

research statement

statement of purpose

I understand what a CV is now, but is a cover form the same thing as a cover letter? Can these documents be generic? Is there a difference between statement of interest and statement of purpose? Is there somewhere I can find examples of these so I know what the difference is?