The main difference between "a lot of" and "lots of" is that "a lot of" is considered to be more formal or used in more formal writing, while "lots of" is considered more casual and informal.
Another difference is that "a lot of" is used with singular nouns, while "lots of" is used with plural nouns. For example, "I have a lot of homework to do" (singular noun) versus "I have lots of books to read" (plural noun).
Both phrases are used to indicate a large quantity or amount of something.
