Downhill means moving toward the bottom of a slope or hill, like when you ride your bike down a steep street or ski down a mountain. The opposite is uphill, which requires effort and energy. Going downhill usually feels easier because gravity does most of the work for you.

The word also describes something that's getting worse or declining. If someone says a situation is going downhill, they mean it's deteriorating or heading in a bad direction. A student's grades might go downhill if they stop studying, or a friendship might go downhill if people stop being honest with each other. When a business is going downhill, it's losing money and customers.

Interestingly, people also say something is all downhill from here to mean the hardest part is over and everything ahead will be easier, like reaching the top of a mountain and knowing the rest of the hike is downhill. But the same phrase can sometimes mean the opposite: that things will only get worse from this point. You usually need to figure out which meaning someone intends from the context of the conversation.