There are basically three methods which we can override.

1. Create
2. Write
3. Unlink

class Campus(models.Model):
    _name='campus'    
    @api.multi
    def unlink(self,values):
        campus_unlink = super(Campus,self).unlink()
        return campus_unlink

The above code snippet is for unlink or delete an entry.

You can find other methods from here: http://learnopenerp.blogspot.com/2017/11/how-to-override-odoo-functions.html