A generic grouping, other models m2m this.

models.py

class Group(models.Model):
    """
    A generic grouping, other models m2m this.
    """
    parent = models.ForeignKey('self', null=True, blank=True, related_name="children")
    slug = models.SlugField(max_length=100, help_text="The slug field.", default="")
    name = models.CharField(max_length=100)

    def __unicode__(self):
        return u"%s/%s" % (
            (lambda g: g.parent if g.parent else "")(self),
            self.slug
        )

unicode() returns easy to read names like:

/parent/child