DOI stands for Digital Object Identifier. It's a unique alphanumeric string assigned to a digital object, like a journal article, book, or dataset, to provide a permanent and reliable link to its location on the internet. For example, a DOI might look like 10.1000/xyz123. The prefix (10.1000) identifies the organization or publisher, while the suffix (xyz123) is specific to the object. DOIs are widely used in academic and research contexts to ensure consistent access to digital content.