What does the related_name parameter in a Django model signify and how does it affect relationships between models?

The related_name parameter in Django is used in model fields that create relationships between models (for example, ForeignKey, ManyToManyField, OneToOneField). It sets the name of the reverse relation — that is, the attribute name through which you can access related objects from the opposite side of the relationship.

Without specifying related_name, Django automatically creates a reverse relation name, usually the model name in lowercase with a _set suffix.

Example:

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name='books')
    title = models.CharField(max_length=200)

Now, with an author object, you can get all books of this author via author.books.all(). If related_name was not specified, you would need to use author.book_set.all().

Thus, related_name improves readability and convenience when working with reverse relations between models.