Which of the following is NOT a description of fibrillation?

Fibrillation is characterized by rapid and irregular contractions of muscle fibers, particularly in the heart, resulting in ineffective blood pumping. The focus is on the nature of muscle contractions being chaotic and uncoordinated.

The choice referring to "large muscle spasm" does not fit the definition of fibrillation. Fibrillation typically describes small-scale, rapid twitching at the level of individual muscle fibers or localized groups of fibers, rather than large muscle spasms which involve broader groups of muscles contracting in a more coordinated manner. Unlike large muscle spasms, which may be visible and affect larger areas of muscle, fibrillation is usually a more subtle and uncontrollable twitching.

The other options accurately describe aspects of fibrillation, such as involuntary muscle contraction, localized contraction, and minor muscular twitching, all of which highlight the erratic and uncontrolled nature of fibrillation as opposed to organized, larger-scale muscle contractions.