A viral titer is the lowest concentration of a virus that still infects cells. To determine the titer, several dilutions are prepared, such as 10, 10, 10, ... 10.
The titer of a fat is the temperature, in degrees Celsius, at which it solidifies. The higher the titer, the harder the fat. This titer is used in determining whether an animal fat is considered tallow (titer higher than 40 °C) or a grease (titer below 40 °C).