The tubal tonsil is one of the four main tonsil

Tonsil

Palatine tonsils, occasionally called the faucial tonsils, are the tonsils that can be seen on the left and right sides at the back of the throat....

 groups which include the Palatine tonsil, the Lingual tonsil, the Pharyngeal tonsil, and the Tubal tonsil.

The tubal tonsil is very close to the torus tubarius

Torus tubarius

The base of the cartilaginous portion of the Eustachian tube lies directly under the mucous membrane of the nasal part of the pharynx, where it forms an elevation, the torus tubarius, the torus of the auditory tube, or cushion, behind the pharyngeal orifice of the tube...

, which is why this tonsil is sometimes also called the tonsil of (the) torus tubarius. Equating the torus with its tonsil however might be seen as incorrect or imprecise.

It is located posterior to the opening of the Eustachian tube

Eustachian tube

The Eustachian tube is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi...

 into the nasopharynx

Nasopharynx

The nasopharynx is the uppermost part of the pharynx. It extends from the base of the skull to the upper surface of the soft palate; it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent .-Lateral:On its lateral wall is the pharyngeal ostium of the...

.