The torus is one of the figures that Lacan analyzes in his study of topology.
In its simplest form, it is a ring, a three-dimensional object formed by taking a cylinder and joining the two ends together.
Lacan's first reference to the torus dates from 1953, but it is not until his work on topology in the 1970s that it begins to figure prominently in his work.
The topology of the torus illustrates certain features of the structure of the subject:
One important feature of the torus is that its center of gravity falls outside its volume, just as the centre of the subject is outside himself; he is decentred, ex-centric.
Another property of the torus is that "its peripheral exteriority and its central exteriority constitute only one single region."
This illustrates the way that psychoanalysis problematises the distinction between "inside" and "outside". (see extimacy).