How much do research papers in arXiv count (for graduate applications)? Wikipedia states that 'Although the arXiv is not peer reviewed, a collection of moderators for each area review the submissions.'

If a paper is not published in any other publication, does it means that it will not contribute to your C.V. when you are applying for an MS or PhD program? Because on arXiv it is not reviewed specifically implies that it does not have the same weight as compared to other publication.
Having a paper that was not peer reviewed but is available from arXiv will help you just as much, and in exactly the same way, as having a paper that was not peer reviewed and is available from any other easily accessed online source. The main things that are important are that:


You have written a paper (according to some definition of "paper").
The paper can easily be accessed and looked at by anyone wishing to evaluate your strength as a grad school applicant.


Note that the value of such a paper to your admission prospects can actually be negative if it is clearly of very poor quality, shows delusional tendencies (e.g., a paper with the title "A simple proof of the Riemann Hypothesis"), or comes across as a dishonest attempt to create a false impression that you have done something important when clearly you haven't. Setting aside such obvious exceptions, an arXiv paper will probably have a positive, but in most cases not very large, value for your applications.