Its essentially how many times an audio stream sends out data over a set period of time.
Its kinda the audio equivalent of Frames per Second. The more you have, the smoother the transition from one frame to the next. A higher number of frames gives a smoother experiance.
As such, a 192Khz Sample Rate samples [or more simply, outputs] data from an audio stream more often, giving a more accurate audio playback.
http://en.wikipedia.org/wiki/Sampling_rate
The graph kinda shows how it works; the more often you sample, the more exact the audio output will be.
It is worth noting, if the audio source is sampled at "X" sample rate, and your are outputting at "2X" sample rate, you won't get any real increase in quality.
And its worth noting, only a few cards support 192KHz output for the PC [and even then, thats normally limited to the front outputs]. I don't think any Creative card supports 24-bit, 192Khz yet either...