Understanding DOIs.
Answer
A Digital Object Identifier (DOI) is a string of numbers, letters and symbols used to uniquely identify an article or document and provide it with a permanent web address. When citing a source with an available DOI, it is highly recommended to include it in your reference list for accurate identification. DOIs can typically be found near the article details, although their placement may vary, or be in the page header or footer of downloaded PDFs. Not all articles possess a DOI though, so don't be concerned if you can’t locate one for your reference.
The example below shows what a DOI might look like:
https://doi.org/10.5860/crl.82.1.7