Domain Events are one specific type of Event used for notifying local or remote Bounded Contexts of Domain changes.

Vaughn Vernon defines a Domain Event as:

An occurrence of something that happened in the domain.

Eric Evans defines a Domain Event as:

A full-fledged part of the Domain Model, a representation of something that happened in the Domain. Ignore irrelevant Domain activity while making explicit the events that the Domain Experts want to track or be notified of, or which are associated with state change in the other Model objects.

Martin Fowler defines a Domain Event as something that:

    Captures the memory of something interesting which affects the Domain.

Examples of Domain Events in a web application are UserRegistered, OrderPlaced, UserRelocated, and ProductAdded.