1. a small, strong bag carried on the back or over the shoulder, used especially by soldiers and walkers.
Word Originlate 17th century: from French havresac, from obsolete German Hafersack, Habersack, denoting a bag used by soldiers to carry oats as horse feed, from Hafer, dialect Haber ‘oats’ + Sack ‘sack, bag’.
A haversack, musette bag, or small pack is a bag with a single shoulder strap. Although similar to a backpack, the single shoulder strap differentiates this type from other backpacks. There are exceptions to this general rule. Wikipedia