temperatures important to cooking

This is my favorite meat-doneness temperature chart.

Water:

• Freezes/thaws at   0°C   32°F
• Boils/condenses at   100°C   212°F

Food safety "danger zone":

• Keep hot food hot, and cold food cold.
• Maintain cold food at ≤   5°C   41°F
• Maintain hot food at ≥   57°C   135°F

Temperature points for other foods:

• Butter browns at   130°C   266°F
• Egg whites (albumin) coagulate at   61-83°C   141-183°F
• Egg yolks thicken at   65-70°C   149-158°F

temperature proxies

In the real world, cooks usually don't stop to use a thermometer. Rather, they get to know certain visual or auditory cues that suggest a certain temperature has been reached.

• great demonstration of different temperature proxies when preheating a pan | Minute Earth

The mist point. A little before heated water begins to simmer (~90°C), some visible mist will appear just above the water. Colloquially people might call this 'vapor' or 'steam', but technically these terms only describe fully-gaseous version of water, which is invisible. The formal term for the visible droplets is 'mist' or 'fog'. The point at which visible droplets begins to appear varies based on temperature and atmospheric pressure, so it's a little less precise of a signal than other temperature proxies.