idea developed in the 1930
's by Marcel Duchamp
and published in 1945
The word is French and means ultratiny or ultrathin; almost but not completely insubstantial.
Infra-mince, Duchamp declared, cannot be defined, but can only be described by examples, such as the difference in displaced volume between a clean shirt and the same shirt worn once, or the taste of one's mouth lingering in exhaled smoke.
Infra-mince was a new way to think about physical and temporal dimensions (decades before Mandelbrot discovered fractals). Holes in some of Duchamp's artwork link the 2nd to the 3rd dimension. Sometimes he shot the holes out with bullets, echoing infra-mince again in the delay between the sounds of the shot and the impact.
Duchamp's larger point was that Art in the world at large is small and insubstantial and only allows one to see things a tiny bit more clearly. Art would not reform politics, as had been hoped, nor emancipate society. This postwar resignation laid the groundwork for the transition from art about objects to art about ideas. In a word, Conceptualism.
Inframince is also the title of part of a posthumous collection of Duchamp's notes published by Paul Matisse.
The Shock of the New by Robert Hughes