noun
rain cover; rain fly
Specifically the waterproof outer layer of a tent or backpack, designed to keep rain out.
テントの雨蓋をしっかり張って、雨に備えた。
I set up the tent's rain fly securely to prepare for rain.
noun
pocket flap
The flap that covers a pocket opening, often on outdoor or military clothing, to keep rain out.
このジャケットの胸ポケットには雨蓋が付いている。
This jacket has a flap over the chest pocket.