The journal to which I have submitted my research paper has asked for an ORCID iD. What is this ORCID iD? Why is it so important for the journal?

ORCID is a non-profit organization that issues unique identifiers to individuals who register on their site. This unique identifier is a 16-digit number that can be associated with all the research output generated by a scientist. Thus, ORCID iD avoids any ambiguity about who a researcher is (e.g., two scientists may have the same exact name) and which body of academic research he/she belongs to. This also addresses the issue of name change, as some researchers may change their surnames after marriage. Additionally,  issues pertaining to the inconsistency in the first name abbreviation or the order of the name of a researcher is also taken care of by an ORCID id. Many journals now ask authors to provide their ORCID ids when they submit their manuscripts. This helps journals associate the authors of a paper with their respective unique identifiers.

According to an editorial in Nature in addition to proving researchers with unique identifier, ORCID aims to provide each researcher with “a constantly updated ‘digital curriculum vitae’ providing a picture of his or her contributions to science going far beyond the simple publication list”. The same editorial also highlighted the fact that in addition to tagging the contributions that scientists make to papers, “could also be assigned to data sets they helped to generate, comments on their colleagues’ blog posts or unpublished draft papers, edits of Wikipedia entries and much else besides”.

Coming to your next question about why is it so important for the journal-

In an open letter on 1^st  January 2016 eight renowned publishers, including the Royal Society, the American Geophysical Union, Hindawi, the Institute of Electrical and Electronics Engineers, PLOS, and Science, stated that they were committed to requiring all authors in their journals to have an ORCID id.  Currently, over 50 publishers have signed this letter. Additionally, more than 2000 publishers include ORCID id’s in their Crossref metadata, and well over 7000 journals request and include id’s in submission and publication. An ORCID id is a positive step toward implementation of good publishing practices across publishers. Therefore, providing your ORCID id is important to publishers.