A DOI (Digital Object Identifier) is a unique series of letters and numbers that are often assigned to electronic sources such as journal articles and books.
Here is an example: https://doi.org/10.1187/cbe.21-09-0237
This DOI example (https://doi.org/10.1187/cbe.21-09-0237) links to a scholarly article about STEM community college students.
DOIs are more permanent than URLs, so they are preferred in citations.
