Simmering

Simmering is defined as to cook food gently in water that is just below the boiling point, that is at or below 100°C or 212°F, but higher than poaching temperature. To keep a pot simmering, the water should first be brought to a full boil, and then heat source is dimmed so as bring down the temperature of the water to a point where the formation of steam bubbles has all but ceased, typically a water temperature of about 94°C (200°F). Simmering is usually a rapid and efficient method of cooking.

Normally eggs and meats are simmered rather than boiled.  For simmering, normally covered pans are used. Alternatively slow cookers such as electric appliances that simmer foods at low temperatures for 4 to 12 hours are also used. 

Although meat is simmered but health experts recommend a caution when using a slow cooker for meat and other foods prone to bacterial growth at warm temperatures.  Usually cooks keep the food to be simmered refrigerated until just before cooking. 

Although poaching, simmering and boiling are similar things, there is a difference of liquid temperature that make these three forms different from each other. In poaching the temperature of the liquid should be 160 degrees to 180 degrees F, while for boiling the temperature range is to be absolute 100 degrees Celsius (222 degrees F) as compared to 185-200 degrees F in simmering.