Interestingly enough, a single SEO campaign can alter the face of the SERP when you know how to execute entity-focused SEO campaigns.

Wikipedia entries are another example of entities. Wikipedia provides a great example of information associated with entities.

As you can see from the top left, the entity has all sorts of attributes associated with "fish," ranging from its anatomy to its importance to humans.

While Wikipedia contains many data points on a topic, it is by no means exhaustive.
What is an entity?

An entity is a uniquely identifiable object or thing characterized by its name(s), type(s), attributes, and situs slot online relationships to other entities. An entity is only considered to exist when it exists in an entity catalog.

Entity catalogs assign a unique ID to each entity. My agency has programmatic solutions that use the unique ID associated with each entity (services, products, and brands are all included).

If a word or phrase is not inside an existing catalog, it does not mean that the word or phrase is not an entity, but you can typically know whether something is an entity by its existence in the catalog.

It is important to note that Wikipedia is not the deciding factor on whether something is an entity, but the company is most well-known for its database of entities.