What is tube rolling?

What is tube rolling?
One of the oldest of audio addictions in the quest for perfect sound. the addiction is gradual and eventually leads to bankruptcy, but at a much slower pace than power cables, interconnects, and speaker cables!
While others have clearly defined tube rolling, I would like to add the benefit of NOS tubes. The difference in sound quality you will experience is astounding. Unfortunately this may be somewhat design dependant and not 100%. I would recomend numerous specific inquiries before spending hard earned cash'
Because tube swapping, tube changing, tube trying, tube experimenting all sound lame.
What would you call it?
Why is it calling rolling? It's a colloquial term. Why is browsing the world wide web called "surfing"? Don't think about this too hard.