What does it mean to fork on GitHub?
After few explorations, In my understanding, it is related to contribution.
Fork means to make a copy of the repository (the one being forked) into my own github account. If I want to fork the official jQuery repository, then I would go to https://github.com/jquery/jquery and hit the "Fork" button and GitHub will copy the repository (jquery) to my account (http://github.com/sanjaykhadka). Then a copied version of that repository will be available to me at http://github.com/sanjaykhadka/jquery
Now I can make whatever the changes I wish to make to my repository and then send a pull request to the original repository (jQuery's repository), asking the jQuery team to merge my changes into their original repository.
Did I understand it properly, or does it mean something more or something else?
Answer
Yes, you are absolutely right. When i teach others GitHub, i would like to explain the concept via an example. Lets take a scenario in which the teacher is conducting an MCQ in his class. He usually make copy of the question paper and distribute it (Forking) to his students so that they can work on it and mark the correct answer. The teacher still has the master copy. On the completion of the test he can collect the copies from students so that he can assess it(Pull request).
Simply just like it. Forking is a concept of making copy of the main repository to your account so that you can make modifications in it. You can Submit pull request to the main repository with the modifications. It will make sure that the main repository is prevented from unwanted changes.