Can you explain what is meant by the term 'entity' in the context of databases or object-oriented programming?

In the context of databases and object-oriented programming (OOP), an entity is an object or element that has a unique identity and is characterized by a set of properties (attributes).

In a database, an entity usually corresponds to a table, where each row is an instance of the entity with a unique key (e.g., ID). In OOP, an entity is a class or object that models a real or abstract object with state and behavior.

For example, in a library management application, an entity could be "Book" with attributes: title, author, ISBN. In code, this would be a class:

class Book {
  final String title;
  final String author;
  final String isbn;

  Book(this.title, this.author, this.isbn);
}

Thus, an entity is a key building block for modeling data and application logic.