Moment form is defined as "a mosaic of moments", and, in turn, a
moment is defined as a "self-contained (quasi-)independent section, set off from other sections by discontinuities" (Kramer 1988, 453).
The concept of moment form, and the specific term, originated with the composition
Kontakte (1958–60) by Karlheinz Stockhausen (Stockhausen 1963a, 189; Stockhausen 1963b, 250).
A "moment", in Stockhausen's terminology, is any "formal unit in a particular composition that is recognizable by a personal and unmistakable character." It can be either an indivisible
Gestalt, a structure with clear components, or a mixture of the two; and it can be static, or dynamic, or a combination of the two. "Depending on their characteristics, they can be as long or as short as you like" (Stockhausen 1963a, 200).
"Moment
forming", on the other hand, is a compositional approach in which a narrative overall line is deliberately avoided. The component moments in such a form are related by a nonlinear principle of proportions. If this system of proportions exhausts a set of possibilities, the form is said to be "closed"; if not, or if the series of proportions is not finite, then the form is "open".
Moment form does not necessarily avoid perceptible goal-directed processes. "They simply refuse to participate in a globally directed narrative curve, which is, naturally, not their purpose" (Dack 1999). In Stockhausen's words, works with this property
Source:
Wikipedia 
