Peritonsillar Abscess. Peritonsillar abscess (also known as quinsy) is a pus-producing infection occurring in the cavity at the back of the throat, near the tonsils.Quinsy is usually a complication of tonsillitis, a bacterial infection of the tonsils.The infection may spread to the soft palate (the back of the roof of the mouth) or may travel down the throat into the chest.uinsy is usually a complication of tonsillitis, a bacterial infection of the tonsils. The infection may spread to the soft palate (the back of the roof of the mouth) or may travel down the throat into the chest.