Celsius/ˈselsiəs/ Definition 1 of 1Pro Tip 1/3Temperature Context Celsius is mostly used in scientific contexts or countries using the metric system. The patient's temperature was recorded at 38 degrees Celsius. Pro Tip 2/3Global Standard Most countries use Celsius for weather temperature, except the United States. It's going to be 30 degrees Celsius this afternoon. Pro Tip 3/3Freezing Point Understand that 0 degrees Celsius is the point where water freezes. The weather forecast predicts temperatures below 0 degrees Celsius tonight.