DOI stands for digital object identifier. It is a unique set of numbers and letters that is assigned to each journal article, and sometimes, ebooks. Think of it like the serial number for your car or laptop; it identifies that unique item.
Here is an example of a DOI for an article published in the Journal of the Academy of Nutrition and Dietetics.
The DOI will usually be located somewhere on the first page of an article. In a database, it will be somewhere in the record for the article or ebook.
If you don't see a DOI for your article, you can check for it on Crossref, and use "search metadata" with the title. If the article has a DOI, it should be listed.
The main citation styles used at KPU require that you include the DOI for the item you are citing, if there is one available. Note that in the most recent editions of Chicago, MLA, and APA style, DOI's are written as links, with this prefix: https://doi.org/.
If you are using a citation generator, be sure that it includes a hyperlinked DOI.