Schrödinger cat is a thought experiment, often used to illustrate parts the Quantum Theory. (I did several experiments with/on Quantum Erasers; and parts of the Quantum Theory itself, and I used this example to partially illustrate the Theory to class mates.)
I found the wiki page on this pretty useful, so I won't re-type what's on the wiki:
One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter, there is a tiny bit of radioactive substance, so small that perhaps in the course of the hour, one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges, and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.
It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.[3]
(
http://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat )
E: I also did a report on the "Double-slit experiment", you may want to read about it too.
http://en.wikipedia.org/wiki/Double-slit_experiment (Double-slit is damn epic, I've done it myself and took pictures too. :D )
E2:
http://www.youtube.com/watch?v=DfPeprQ7oGc
