On Temperature

Here is something, excerpted and edited, from wikepedia regarding temperature:

In physics, temperature is a physical property of a system that underlies the common notions of hot and cold...
On the macroscopic scale, temperature is the unique physical property that determines the direction of heat flow between two objects placed in thermal contact. If no heat flow occurs, the two objects have the same temperature; otherwise heat flows from the hotter object to the colder object...
On the microscopic scale, temperature can be defined as the average energy in each degree of freedom in the particles in a system- because temperature is a statistical property, a system must contain a few particles for the question as to its temperature to make any sense. For a solid, this energy is found in the vibrations of its atoms about their equilibrium positions. In an ideal monatomic gas, energy is found in the translational motions of the particles; with molecular gases, vibrational and rotational motions also provide thermodynamic degrees of freedom.

The wikepedia site has some nice pictures of thermal motion.
http://en.wikipedia.org/wiki/Temperature