noun, noun or participle which takes 'suru', intransitive verb
night encampment; bivouacking
Refers to setting up camp for the night, often in a military or outdoor context. Can be used as a noun or as a suru-verb.
部隊は山中で夜営した。
The troops bivouacked in the mountains.
夜営の準備を始めよう。
Let's start preparing for the night encampment.
野営 is a more general term for camping outdoors, while 夜営 specifically emphasizes camping at night.
Compound of 夜 (night) and 営 (camp, manage). The exact historical derivation is uncertain, but the meaning is transparent from the kanji.