Calorimetry
Definition
Measuring heat flow in a reaction using an insulated container called a calorimeter: basically a very careful thermometer experiment.
Technical definition
Calorimetry is the experimental measurement of heat transfer during physical or chemical processes, typically using q = mc deltaT for solution calorimeters or q = C deltaT for bomb calorimeters, assuming no heat exchange with the surroundings.
Example
Dissolving ammonium nitrate in a coffee-cup calorimeter and measuring the temperature drop lets you calculate the heat of solution.
Common confusion
A coffee-cup calorimeter measures heat at constant pressure (giving enthalpy change), while a sealed bomb calorimeter measures at constant volume (giving internal energy change). They are not interchangeable.