I have no real definitions of the things you are puzzled about, but I can still explain a few things. Let me, first, get rid of peer-review because it is easy. By the past, journal editors used to read submitted article to the journals and issue a decision either to publish or reject. As this was felt to be too biased and subjective, peer-review entered the scene. It is simply the fact that the role of the editor has changed, seeking the help of peers in the profession to assess the submitted article, with the role of the editor reduced to cases where siding with publishing or rejecting is needed. This is something internal to the workings of a journal. Peer-reviewing has become the sine qua non of publishing. Now, the difference between national and international journal has to do with the quality of publications in a journal. Usually, journals that may start as national and cannot compete with international ones in terms of research quality, maybe because they allow less good quality to be published. If they want to attain an international status, they need to implement measures of rigor and quality. And here comes indexing, which is a kind of quality assessment. There are many levels of indexing, starting from abstract indexing (Elsevier offers that, I think) to whole article (ISI). ISI offers (under Web of Knowledge) a classification of journals into 3 or 4 categories, each assessed through its impact factor and number of citations per journal.

I hope this could prove useful to you. You may google all these things for more documented answers.

Journals are also categorised into four quartiles: Q1, Q2, Q3 and Q4. Journals in Q1 and Q2 are considered top-tier journals having higher impact factors while lower-tier journals are classified as Q3 and Q4 having lower impact factors.

Thank you for the reply

Many academic bodies ask for the classification of a national and international journal. I was trying to find the definition of the same.