These are the original OpenAlex Concepts, which are being deprecated in favor of Topics. We will continue to provide these Concepts for Works, but we will not be actively maintaining, updating, or providing support for these concepts. Unless you have a good reason to be relying on them, we encourage you to look into Topics instead.
Concepts are abstract ideas that works are about. OpenAlex indexes about 65k concepts.
The Canonical External ID for OpenAlex concepts is the Wikidata ID, and each of our concepts has one, because all OpenAlex concepts are also Wikidata concepts.
Concepts are hierarchical, like a tree. There are 19 root-level concepts, and six layers of descendants branching out from them, containing about 65 thousand concepts all told. This concept tree is a modified version of the one created by MAG.
A score is available for each concept in a work, showing the classifier's confidence in choosing that concept. However, when assigning a lower-level child concept, we also assign all of its parent concepts all the way up to the root. This means that some concept assignment scores will be 0.0. The tagger adds concepts to works written in different languages, but it is optimized for English.