Meaning of anacrusis

an•a•cru•sis

Pronunciation: (an"u-kr'sis), [key]
— pl. -cru•ses
  1. an unstressed syllable or syllable group that begins a line of verse but is not counted as part of the first foot.
  2. the note or notes preceding a downbeat; upbeat.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.