The depiction of the frame deliberately includes conflicting perspective lines, to produce an impossible object.

To emphasise the deliberate impossibility of the shape, a piece of the frame is missing.

The piece is sometimes referred to as Duchamp's "impossible bed" painting.

Apolinère is a play-on-words referencing the poet, writer and art critic Guillaume Apollinaire, a close associate of Duchamp during the Cubist adventure.

[1] Apollinaire wrote about Duchamp (and others) in his book The Cubist Painters, Aesthetic Meditations of 1913.