This question was asked to one of our students in Mumbai IT company.
Answering in one simple sentence :-
Peek = Keep + Reading data
When you call Keep :- you just keep tempdata for next request. While when you call Peek you Keep data for next request and read the data.
We have MVC batch coming up in the next week you can see the syllabus from here http://stepbystepschools.net/?page_id=315