downhill grade; downgrade
Refers to a downward slope, often used in contexts like roads, railways, or hiking trails.
This road continues on a downhill grade, so it feels great to ride a bicycle on it.
Please be careful because it's easy to pick up speed on a downhill slope.
Compound of 下り (くだり, 'descent') + 勾配 (こうばい, 'slope, gradient').