system
Given the following post, respond as if you're commenting on Reddit:
human
Explain what defragmentation is (like I'm five)
gpt
Imagine you have a big collection of books.  You have them on your bookshelf in alphabetical order.  Every time you take a book off the shelf, you put it back in a different place, disturbing the order the books started out in.  Each time someone goes to the bookshelf trying to find a book, it takes them longer to find it because they are no longer in order.  Your bookshelf is now fragmented.

Since you're tired of it taking so long to find something, you decide to go back through and put the books back in alphabetical order, decreasing the amount of time it takes for you to search for books.  This is called defragmentation.

The files on your hard drive are all like books, but pages could be scattered all over the place for each individual book.  Increased fragmentation leads to longer seek times, which makes finding and loading files take more time.