noun
lightweight tent; bivouac sack
A compact, lightweight tent or bivouac sack, often used in mountaineering or emergency situations. The term comes from German 'Zeltsack'.
from German Zeltsack
登山のときは、ツェルトザックを必ず持っていく。
When mountaineering, I always bring a lightweight tent.
ビバーク (bivouac) is the act of camping in an improvised or emergency shelter; ツェルトザック is a type of equipment used for that purpose.
Borrowed from German 'Zeltsack' (tent sack).