Noun
irreducible complexity (uncountable)
(biology, pseudoscience) The proposition that complex organs such as eyes and flagella must have started existing in their current form; i.e., that they cannot have evolved from previous, less complex stages.
Irreducible complexity is not an argument that evolution does not occur, but rather an argument that it is "incomplete". Source: Internet
Irreducible complexity may not actually exist in nature, and the examples given by Behe and others may not in fact represent irreducible complexity, but can be explained in terms of simpler precursors. Source: Internet