Meaning
A glass thermometer with a bulb at the bottom and a red line rising up the scale. It stands for temperature in general, from the weather to body heat.
People reach for it during heatwaves, cold snaps and when someone is running a fever, often with 🥵, 🥶 or 🤒: “Feels like an oven out there 🌡️ stay inside if you can.” It also works for figurative heat, like a debate that is getting tense.